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Orientational and positional ordering of nanorods in the lamellae phase of diblock copolymers has been investigated using a simple theoretical model and dissipative dynamics simulations. Orientational order parameter and local concentration profiles of nanorods are calculated numerically and extracted from computer simulations data for different values of the nanoparticle length and different number of the interaction sites in the model nanorod. The predictions of the molecular theory are compared with the results of computer simulations. It has been found that the nanorods are orientationally ordered in the boundary region between the domains and the orientational order parameter changes its sign at the domain wall. At the same time there exists some quantitative discrepancy between theory and computer simulations which is partially removed when a similar model of a nanorod is employed both in the molecular theory and in coarse-grained molecular dynamics simulations.

We have investigated the origin of spontaneous polar ordering in smectic liquid crystals in the framework of molecular-statistical approach. The polar order parameter is introduced as p = P / ( ρ μ...

This article honours Michael Baer on the occasion of his 80th birthday and celebrates his scientific contributions to non-adiabatic chemical physics. This undertaking prompts the presentation of a first principles molecular theory of the genetic code. Jacques Monod's classic essay, 'Chance and Necessity', is exercised as a platform for this discussion. In particular the controversial concept of teleonomy is considered and evaluated in relation to modern developments in chemical physics.

In a recent work, we performed free-energy analyses for hydration of benzene by conducting QM/MM-ER simulations, where the total solvation free energy was decomposed into contributions and . is the...

Orientational ordering of rod-like nanoparticles in the lamellae phase of diblock copolymers has been considered theoretically using the model of a nanoparticle with two interaction centres. It has been shown that strongly anisotropic nanoparticles order spontaneously in the boundary region between the blocks where the orientational order is induced by the interface and by the interaction with monomer units in different blocks. The nematic order parameter possesses opposite signs in adjacent blocks which means that the nanorods are aligned parallel or perpendicular to the boundary between the blocks on different sides of their interface. Concentration and nematic order parameter profiles have been calculated numerically for different values of the nanoparticle length and compared with the results of recent computer simulations and with the results of the previous molecular theory based on nanoparticles of spherical shape.

Sum-frequency generation spectroscopy is a powerful tool for analysing molecular species and orientation configurations on a surface or an interface. In addition to conventional vibrational resonant techniques, the electronic resonant (electronic sum-frequency generation [ESFG]) ones have been developed recently. We have established the theoretical formulation of ESFG spectroscopy based on the susceptibility approach, considering resonances with both symmetry-allowed and symmetry-forbidden electronic excited states; derivatives of transition dipole moments and vibronic couplings beyond the Condon approximation were included. With the aid of density functional theory computations, simulated ESFG spectra in resonances with both types of excited states of acetone are demonstrated.

Furoxan-fused pyrenes and their dinitroso derivatives (obtained by furoxan ring opening) are considered for density functional treatment at the level of B3LYP/6-31G(d,p). Embedded benzofuroxan moiety in the furoxan-fused pyrene system is thought to undergo ring opening and reclosure process analogously to benzofuroxan itself. The stabilities, structural features, NICS(0) values, IR, and UV-VIS spectral aspects, etc., are investigated comparatively for these isomeric furoxan-fused pyrenes and their isomeric dinitroso derivatives.

A new approach for formulating the self-interaction correction, referred to as the Fermi-Lowdin orbital-based self-interaction correction (FLO-SIC), is briefly reviewed and applied to the Fe(II)-po...

A molecular-statistical theory describing the nematic liquid crystals (LCs) with spherical inclusions (or point defects) is proposed. At given size of inclusions and nematic order parameters at the...

We examine the one-centre integrals used in semiempirical molecular orbital theory, for the elements H–Ne. The currently used parameters do not provide good estimates for the relative energies of ionised states of atoms. Directly calculating the one-electron integrals Uss and Upp with coupled-cluster theory and fitting the two-electron repulsion integrals Gss and Gpp to accurate coupled-cluster ionisation curves improves this behaviour. Since all the remaining parameters can be derived from these, the number of fitted variables is reduced from seven to two. The two-parameter model provides qualitative agreement with coupled-cluster theory for all ionisation potentials (IPs) and the principal electron affinity (EA). To obtain quantitative agreement for the principal IP and EA, Uss and Upp are included as variables in a four-parameter model. We discuss the new parameters and implications for the development of new, consistent semiempirical Hamiltonians.

Electron orbitals are ubiquitous in chemistry for the description of bonding and molecular properties. This article outlines a theoretical framework for the generation and application of orbitals for the analysis of the electronic structure, chemical bonding, and magnetic properties of metal complexes from relativistic quantum chemical wavefunction calculations. Examples from the author’s research of f-element complexes are used to illustrate these concepts, with emphasis on open-shell systems.

This paper presents the definition and characterisation of quantum molecular polyhedra. They are taken here within the description of a single molecule, using quantum molecular orbital (MO) density functions as vertices. The formalism and parameters associated to these mathematical structures are analysed. Picture Drawn by Pep Camps, Girona (2015). © 2015 Taylor & Francis

We review various proposed molecular mechanisms for tilting of rod-like molecules in the smectic C phase. We analyse some experimental results, viz. (1) unusual odd–even effects in smectic A to nematic (TAN) and smectic A to smectic C (TAC) transition temperatures and/or maxima in TAC in some homologous series of compounds, (2) occurrence of re-entrant SmA and/or hexatic SmB as lower temperature phases, (3) SmC replaced by SmA when a halogen atom is substituted at the end of one of the chains, (4) suppression of SmC phase at high pressures, and in binary mixtures with dissimilar aromatic cores or chain lengths, (5) induction of SmC phase in mixtures of some structural isomers and (6) some recent all-atom simulations. The results can be understood on the basis of our molecular theory in which the tilting occurs due to the repulsive coulomb interaction between neighbouring molecules having off-axis dipoles with transverse components and freely rotating about their long axes in smectic layers. The model also...

Shungite is presented as a natural carbon allotrope of a multilevel fractal structure that is formed by a successive aggregation of ~1 nm reduced graphene oxide nanosheets. Turbostratic stacks of the sheets of ~1.5 nm in thickness and globular composition of the stacks of ~6 nm in size determine the secondary and tertiary levels of the structure. Aggregates of globules of tens of nanometers complete the structure. Molecular theory of graphene oxide, supported by large experience gained by the modern graphene science, has led to the foundation of the suggested presentation. The microscopic view has found a definite confirmation when analyzing the available empirical appearance of shungite. To our knowledge, this is the first time a geological process is described at quantum level.

We have proposed a new canonical-isokinetic ensemble for efficient sampling of conformational space in molecular dynamics (MD) simulations which leads to the optimised isokinetic Nosé-Hoover (OIN) chain algorithm for atomic and molecular systems. We applied OIN to multiple time step (MTS) MD simulations of the rigid and flexible models of water to demonstrate its advantage over the standard canonical, isokinetic and canonical-isokinetic ensembles. With the stabilising effect of OIN thermostatting in MTS-MD, gigantic outer time steps up to picoseconds can be employed to accurately calculate equilibrium and conformational properties. Furthermore, we developed the atomic version of OIN for MTS-MD of a biomolecule in a solvent potential of mean force obtained at sequential MD steps by using the molecular theory of solvation, aka three-dimensional reference interaction site model with the Kovalenko-Hirata closure (3D-RISM-KH). The solvation forces are obtained analytically by converging the 3D-RISM-KH integral equations once per several OIN outer time steps, and are calculated in between by using solvation force-coordinate extrapolation (SFCE) in the subspace of previous successive solutions to 3D-RISM-KH. For illustration, we applied the multiscale OIN/SFCE/3D-RISM-KH algorithm to a fully flexible model of alanine dipeptide in aqueous solution. Although the computational rate of solvent sampling in OIN/SFCE/3D-RISM-KH is already 20 times faster than standard MD with explicit solvent, further substantial acceleration of sampling stems from making solute evolution steps in a statistically averaged potential of mean force obtained from 3D-RISM-KH. The latter efficiently samples the phase space for essential events with rare statistics such as exchange and localisation of solvent and ligand molecules in confined spaces, pockets and at binding sites of the solute macromolecule, as distinct from MD with explicit solvent which requires enormous computational time and number of steps in such cases. © 2013 Taylor & Francis Group, LLC.

The well-known natural orbitals are defined as eigenfunctions of a one-particle reduced density operator, and can be obtained from a computed density matrix by diagonalization. Similarly, in this article we define the binatural orbitals, which are obtained for a pair of wave functions by a singular value decomposition of a reduced transition density matrix. The pair of states would usually be eigenstates of the electronic Hamiltonian, and the binatural orbitals then serve as a useful tool for the analysis of the transition between these states. More generally, application to any two state functions gives important information as to how the two states differ. Some examples are shown.

The response of liquid crystals to light is very important in applications of liquid crystals in display and memory devices. Experiments have been conducted on liquid crystals doped with photoactive azo compounds, and has been shown that under incident UV radiation such systems can lower the nematic isotropic transition temperature, T NI. In addition, in some mixtures a photo-induced smectic phase is observed, attributable to the change from the trans (longer) isomer to the cis (shorter) isomer in the photoactive dopant. We have previously developed a molecular mean field model, on the assumption that the medium consists of interconverting anti-parallel and parallel pairs, to explain the molecular origin of ‘two lengths’. The model was used to explain double re-entrance, the effect of electric field on T NI, etc. This model has now been modified to include the change between the trans and cis isomer, which is equivalent to an increase in the fraction of parallel (shorter) pairs. The phase diagram calculat...

As an alternative to the conventional solvation models, we propose to use the molecular theory of solvation also known as the three-dimensional reference interaction site model with the Kovalenko–Hirata closure (3D-RISM-KH) as an essential part of a multiscale approach for biomolecular modelling at nanoscale. Based on the rigorous statistical–mechanical foundation, this approach provides a natural link between different levels of coarse-graining details in the multiscale description of the solvation structure and thermodynamics, from highly localised structural solvent and bound ligand molecules to effective desolvation potentials and self-assembling nanoarchitectures. Using the 3D-RISM-KH approach, we study all stages of formation of fibrillar aggregates and amyloid fibrils. We also show that the approach is capable of predicting binding sites for the inhibitors of the pathological conversion and aggregation of prion proteins in agreement with experimental data.

We propose the derivation and calculation of the hydrodynamic slip length from the first principles of statistical mechanics, based on a combination of linear response theory and equilibrium molecular theory of solvation. The slip length obtained is independent of the type of flow and is related to the fluid organisation near the solid surface, as governed by the solid-liquid and liquid-liquid interactions. In a wide range of shear rates and surface-liquid interactions, the slip length is expressed in terms of the Green-Kubo-Nakano relations as a function of the anisotropic inhomogeneous time correlation function of density fluctuations of the liquid in contact with the surface. The presented treatment generalises the phenomenological definition of the friction coefficient and the slip length to a tensor quantity, which reflects an anisotropic nature of an ordered crystalline surface. We derive generic analytical expressions for the liquid-surface friction coefficient and slip length for an arbitrary surface-liquid interaction potential. We further illustrate it by numerical calculations for the case of a laminar flow of several molecular liquids and water, at ambient conditions in contact with the (100) FCC surface of gold, copper and nickel modelled using all-atom or united-atom models for liquids and the Steele potential for crystalline surfaces. The values obtained for slip length range from few to hundreds of nanometres and are consistent with experimental measurements. We also calculate pressure and temperature dependence on the slip length for water in a wide range of these thermodynamic parameters. The information obtained is intended to be used, in particular, to control or manipulate the flow in electrokinetic processes. © 2011 Taylor & Francis.

A novel chromogenic and fluorogenic dye chemosensor was computationally designed using MO theory calculation and synthesized based on donor-π-acceptor unit. This prepared dye sensor showed the selective Ni2+ metal ion sensing effects in optical properties with UV-vis absorption and fluorescence emission. Dye sensor displayed evident absorption changes with Ni2+ ion and highly selective fluorescence quenching effect was determined. But it showed no significant changes upon the addition of other metal ions such as Cd2+, Na2+, Mg2+, Pb2+, Fe2+, Fe3+, Ca2+, Cu2+, Hg2+ and Zn2+

An overview of work on electronic rearrangement in molecular collisions and in particular on combining time-dependent many-electron theory and eikonal methods for nuclear motions is presented. Special attention is given to the time scales present in atomic interactions with kinetic energies from a fraction of an eV to 10 keV, of interest in molecular collisions, atomic collisions with surfaces and transient spectra of electronically excited atoms in a medium. The treatment uses basis sets of travelling atomic orbitals, also adapted for the study of magnetic effects in molecules as gauge origin invariant atomic orbitals. An efficient computational approach to the time evolution of the systems, the relax-and-drive propagation method, is described. Brief descriptions are given of the connection with other approaches suitable for transient phenomena in molecular interactions.

Higher order singular value decomposition is studied in the context of quantum chemistry, with particular focus on the decomposition of the 𝒯 2 amplitudes obtained from second order Moller Plesset perturbation (MP2) theory calculations. Our test calculations reveal that HOSVD transformed amplitudes yield considerably faster convergence in MP2 correlation energy, both in terms of amplitude and orbital truncation. Also, HOSVD orbitals display increased bonding/antibonding character compared to Hartree–Fock orbitals. In contrast to canonical MP2 theory, the leading amplitudes are those between corresponding occupied–virtual orbital pairs. The HOSVD orbitals are paired up automatically around the Fermi level in decreasing importance, so that the strongest occupied virtual–pair are the highest occupied molecular orbital and lowest unoccupied molecular orbital. We show that in the case of MP2 amplitudes, the HOSVD orbitals are equivalent to the unrelaxed MP2 natural orbitals. The least squares higher order orth...

Valence bond (VB) theory calculations have been performed on a series of small molecules and the bond dissociation energies (BDEs) and Chirgwin–Coulson structure weights have been obtained. The number of electrons included in the VB active space has been varied to include all valence electrons, only valence electrons of the same symmetry as the target bond, or only the bonding electrons. In addition, VB orbitals were either held strictly localized on a particular fragment (fragment localized orbitals) or allowed to delocalize onto neighbouring fragments (overlap enhanced orbitals). Structure weights and BDEs thus obtained were compared to previous breathing orbital VB (BOVB) and experimental results. Although none of the methods used herein give particularly accurate results due to neglect of dynamic electron correlation, including only bonding electrons in the VB active space with the use of overlap enhanced orbitals sufficiently reproduces trends in BDEs and structure weights with minimal computational ...

The elastic theory of liquid crystals can be traced back to the early 1930s, but the origin of the molecular theory of elastic constants must be postponed to more than 30 years later, when Alfred Saupe wrote his famous papers on this subject. At approximately the same time, the seminal works by Priest and Straley also appeared. Since then, several theories have been developed to connect intermolecular interactions to curvature deformations, on a quite different length-scale, in liquid crystals. This field was particularly alive between the end of the 1970s and the beginning of the 1980s, in parallel with experimental investigations. In more recent times, a renewed interest was aroused by the controversy about the second-order splay-bend contribution, which appears in the Nehring–Saupe expression for the deformation energy density. In the first part of the present contribution the molecular theory of elastic constants is briefly reviewed. This paper focuses on the effects of molecular structure on the elas...

H/D and 16O/18O vapor pressure isotope effects (vpies) of water between liquid water and water vapor were reinvestigated by estimating the reduced partition function ratios, rpfrs, of water clusters, (H2O)n, with n up to 100 at the HF/6-31G(d) level of molecular orbital theory. Large water clusters with n = 80−100 resulted in a reasonable estimate of the 16O/18O vpie, which was in contrast to the one for which only small water clusters had been considered. Contrary to this, no appreciable improvement in the H/D vpie reproduction by using large water clusters was observed.

An efficient program for calculating nuclear magnetic shielding tensors at the level of density fitted Hartree–Fock theory is presented. London atomic orbitals are used as AO basis functions, while ordinary Gaussians are employed as auxiliary fitting functions for the density fitting. The errors due to density fitting turn out to be very small. Accuracy and efficiency of the program are demonstrated in calculations on several test molecules.

The electronic structures of pyrimidine and a selection of its halogen-substituted derivatives have been investigated using ultraviolet photoelectron spectroscopy and ab initio quantum chemical methods. Assignments are proposed for all of the features in the PES spectra by comparison with the vertical ionization energies of the molecular orbitals calculated using the partial third-order quasiparticle approximation as applied to electron propagator theory and a corrected density functional method based on the B3LYP functional. The shifts of the outermost five molecular orbitals of the pyrimidine ring structure in the halogen-substituted derivatives with respect to the binding energies of the equivalent orbitals in the parent pyrimidine molecule are discussed as a function of the identity and ring position of the halogen atom.

By examining the natural orbital occupation numbers, it was discovered that unrestricted Moller–Plesset perturbation theory (MP2) can violate N-representability by having natural occupation numbers greater than 2 or less than 0, even though the energy appears well behaved. Analytically, this problem stems from the fact that the MP2 effective one-particle density matrix is dependent on the inverse of the orbital hessian matrix (A′). When a molecular system goes through the point where spin-restricted orbitals become unstable to unrestriction, one of the eigenvalues of the A′ matrix will become 0, making it a singular matrix, thereby causing problems in the relaxed one-particle density matrix and discontinuities in the first order properties such as nuclear forces and dipole moments. Since the new ‘double-hybrid’ density functionals also involve a second-order perturbation expression for correlation using Kohn–Sham orbitals, these functionals also exhibit similar issues near the unrestriction point. The unp...

Asphaltene aggregation reduces bitumen upgrading efficiency by increasing bitumen viscosity and coke formation. Our approach to model asphaltene aggregation involves geometry optimisation by using the Harris approximation implemented in DMol3, followed by a solvation calculation by using the three-dimensional molecular theory of solvation (a.k.a. 3D-RISM) we have developed recently [A. Kovalenko, Three-dimensional RISM theory for molecular liquids and solid–liquid interfaces, in Understanding Chemical Reactivity: Molecular Theory of Solvation, F. Hirata ed., Vol. 24, Kluwer Academic Publishers, New York, NY, 2003, pp. 169–275]. From the Harris approximation, we obtain the Hirshfeld and Mulliken asphaltene atomic charges. The 3D-RISM theory allows one to model solvation at given temperature, solvent density and solvent composition. The theory predicts solvation structure and thermodynamic characteristics, such as the potential of mean force (PMF). We investigate the effect of the Hirshfeld and Mulliken cha...

The origin of δ (Se) is revealed based on the MO theory. The pre-α effect in H 2 Se, defined in the text, is the generation of double σ(Se─H) and σ*(Se─H) through the protonation to spherical Se 2− . The extension of HOMO-n (n = 0, 1, and 2) over the whole molecule of Me 2 Se is mainly responsible for the α effect. The β effect originates not from the occupied-to-unoccupied transitions but from the occupied-to-occupied transitions. The γ effect of the upfield shifts is the results of the subtle balance between two types of transitions. Contributions from each MO (ψ i ) and each ψ i → ψ a transition are evaluated separately, using a utility program (NMRANAL-NH03G).

The molecular theory of Onsager [L. Onsager, Ann. N.Y. Acad. Sci. 51, 627 (1949)] for liquid crystals is developed and extended to describe ordering transitions in systems of generic cylindrically symmetrical molecules. A number of new analytical results are discussed for particles characterised by a general form of the excluded-volume interaction. Our description makes use of the Onsager trial function (OTF) to represent the orientational distribution and degree of anisotropy. Algebraic expressions for the thermodynamic properties, which provide a particularly tractable description of the isotropic–nematic equilibria, are also presented. The degree of orientational order can be represented by a simple cubic equation in the molecular parameters (molecular diameter and aspect ratio) and thermodynamic variables (temperature and number density). Onsager's theory was originally developed at the level of the second virial coefficient; here the Parsons–Lee decoupling approximation is used to describe the higher...

Individual outer valence orbital responses to rotations of the C–C central bond of butane (C4H10) are explored on the torsional potential energy surface. Orbital ionization energies, topologies and momentum distributions for the four most significant butane conformation are presented, as snapshots of the conformational variations. The analysis is based on quantum mechanically generated information from coordinate space and momentum space, a technique called dual space analysis (DSA). By comparison with experimental measurements of photo-electron spectra (PES) for energies and of electron momentum spectra (EMS) for energies and Dyson orbitals, we demonstrate that the individual outer valence orbitals of these conformers response differently to the rotations of the central C–C bond of n-butane. Orbital signatures of other higher energy conformations, such as orbitals la 2 and 5a 1 of conformation D (C2v ), are identified. This finding indicates a co-existence of butane conformations, although the global min...

We investigate isotope effects in dihydrogen systems using the nuclear orbital plus molecular orbital (NOMO) theory, which simultaneously determines nuclear and electronic wave functions without the Born-Oppenheimer approximation. In order to estimate the vibrational averaging bond distances, the analytical energy gradients are used for the NOMO theory. The bond distances of three dihydrogen-bonded systems, namely H3NX+ ··· XBeH, LiX ··· XC2H and H2BX ··· XF for X = H, D and T, are obtained. The X ··· X bond distances decrease with respect to the substitution T → D → H, which is contrary to the behaviour of typical hydrogen bonds. This indicates that isotope effects strengthen the X ··· X bond. This behaviour is analogous to the Ubbelohde effect observed in the solid phase.

Here we examine the connection between high order harmonic generation (HHG) and molecular electronic structure within the strong field approximation (SFA) by surveying the dipole moment between the highest occupied molecular orbital (HOMO) and a plane wave approximation to the continuum state. We take as examples a number of wavefunctions in a Gaussian basis corresponding to hydrogen 1s, and the 2s and 2p x orbitals that are the building blocks for the N2, CO2 and other molecular orbitals. The harmonic dipole moment amplitude and phase is examined as a function of angle between a fixed axis in the frame of the wave function and the continuum electron momentum vector. We then examine, and discuss, the results for a number of molecules where experimental data already exists such as N2, CO2, acetylene and allene with orbitals calculated within a Gaussian basis using the GAMESS program. Concrete predictions can be obtained from this procedure against which measurements can be compared. In this way the validit...

In the microscopic point of view, a decay rate of the nematic liquid crystalline order is formulated in a tractable form on the basis of a projection method, which is calculated by a Monte Carlo simulation of the Gay-Berne particle system. Three types of systems with different particle lengths are studied, where at a sampling during early stage of relaxation process, the decay rate is shown to increase as the length of the particle becomes short. At the system of particles of length with 3 times of a diameter, remarkable increase is observed at a transition to a disordered phase. The relaxation process of an order parameter is also simulated simultaneously in place of an experiment, from which the decay rate at the system with 3 times length is tentatively obtained as a macroscopic estimate by fitting the Monte Carlo curve of the order parameter to an exponential function. Both estimates of the decay rate are compared, where the correspondence is qualitatively good.

We have carried out first-principles molecular dynamics simulations of Al deposition on tris (8-hydroxyquinoline) aluminum (Alq3) layers to investigate atomic geometries and electronic properties of Al/Alq3 interfaces. Al atoms were ejected to Alq3 one by one with the kinetic energy of 37.4 kJ/mol, which approximately corresponds to the average kinetic energy of Al at the boiling temperature of metal Al. The first Al atom interacts with two of the three O atoms of meridional Alq3. Following Al atoms interact with Alq3 rather weakly and they tend to aggregate each other to form Al clusters. During the deposition process, Alq3 was not broken and its molecular structure remained essentially intact. At the interface, weak bonds between deposited Al atoms and N and C atoms were formed. The projected density of states (PDOS) onto the Alq3 molecular orbitals shows gap states in between the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs), which were experimentally observed by ultraviolet photoelectron spectroscopy (UPS) and metastable atom electron spectroscopy (MAES). Our results show that even though the Alq3 molecular structure is retained, weak N–Al and C–Al bonds induce gap states.

Interlayer interaction in the ferroelectric and antiferroelectric smectic phases is developed taking into account the distribution of dipole moment in molecule of liquid crystal. A very important role is played by mutual dislocation of different fragments of molecules inside smectic layer and it plays the key role in dipole-dipole interaction between neighbouring layers. Tilt of molecules in the smectic layer is followed from the ordering of the dipole moments in one direction of one layer. Three ordered phases are found, first is synclinic, second is anticlinic and third is twisted structure. In twisted structure the angle between two layers is 90 degree.

Quantitative structure-activity relationships were obtained for series of methyl benz[a]anthracene and benz[c]acridine molecules. Regression analysis was done on π-electronic indices associated with specified molecular regions of importance named “bay” (Q AB ),“K” (Q K ), “L”(QL), N-heteroatomic position (QN) and superdelocalizability index (SK associated with K-region) of these molecules to correlate with reported experimental carcinogenicity indices. The electronic indices calculated earlier for methyl benz[c]acridines by a self-consistent field molecular orbital theory named ‘two-parameter omega-technique’ are reported from unpublished data. ‘Two-parameter omega-technique’ used successfully for methyl derivatives earlier, was modified to incorporate the N-heteroatom present in benzacridines. Reported log (carcinogenicity indices) for a series of 14 methylbenz[a]anthracenes are found to be positively correlated with Q AB having correlation coefficient (R = 0.65) which is increased to 0.82 by combining t...

Two molecular orbitals: MO7 (29a) and MO13 (23a) have been identified using dual space analysis (DSA) as the signatures of adenine non-planarity (C1 point group symmetry). The non-planarity of adenine has been demonstrated to be from the attachment of the amino group (NH2) to purine rings as well as the non-rigid deformability of the purine ring of adenine. Orbital 29a (3a″ in the planar case), a π-like orbital, is the direct result of the attachment of the amino group to the purine ring. Orbital 23a (23a′ in the planar case) is the result of the deformability of the purine ring in non-planar adenine (NP) and will be experimentally challenging to resolve.

The probability-resolution scheme for partitioning the molecular bond-multiplicities into atomic contributions, suggested by the ‘partial’ atomic channels of the Communication Theory of the chemical bond, is applied to the simplest two-orbital model of a diatomic molecule. It offers a unique perspective upon a degree of the atom involvement in the covalent and ionic interactions with its molecular environment. The row channels generate the atomic contributions to the molecular bond-multiplicity and its covalent/ionic composition, while the atomic column channels give rise to the valence indices of bonded atoms, which reflect their promoted states in a molecule. Plots of the entropy/information bond indicators of atomic partial communication channels are generated over the whole range of the probability of finding an electron on the specified atom, 0 ≤ P ≤ 1, which measures a degree of polarization of the bonding molecular orbital (MO). They are compared with the MO predictions obtained from the same proba...

We recently reported that very compact coupled-cluster wave functions may be generated by selecting the most important configurations, by weight, from the full coupled-cluster wave function. Here, we consider how the choice of orbitals may affect these wave functions in the case of the symmetric dissociation of H2O. We employ unrestricted Hartree–Fock and complete-active-space self-consistent-field orbitals, as well as natural orbitals derived from a coupled-cluster singles and doubles wave function. For a given accuracy, some choices of orbitals can reduce the size of configuration interaction wave functions, but they have little effect on the weight-selected coupled-cluster wave functions.

We present a statistical mechanics approximation scheme for the explicit treatment of spacer‐mediated configurational correlations among the mesogenic units that form a dimer molecule. The approximation is applied to the description of the nematic phase of linear uniaxial dimers interacting via a standard molecular pair‐potential. Transition temperatures, order parameters and pair correlation averages are calculated for different spacer lengths. The results readily reproduce the experimentally observed trends of phase transition thermodynamics and of dipolar correlations deduced from dielectric studies.

Qualitative analysis of the factors governing variation in T c and P s of PbTiO3, KNbO3 and BaTiO3 members of ABO3 perovskite family considering the parameters like tolerance factor, t, electronic configuration, electronegativity, polarizability and character of bonding using molecular orbital theory (MOT) reveals that (i) T c and P s vary inversely with t, (ii) increased interaction between ions decreases t as packing in unit cell increases, (iii) the size of A and B cations and their interaction with oxygen governs the ferroelectric behaviour, (iv) the covalent interaction between A─O and B─O is responsible for the other transitions in the ferroelectric phase and (v) the occurrence of P s is due to the presence of mixed ionic-covalent B─O bonds.

The director response times of pure IPS and VA modes were compared by inserting respective material constant values of practical LC mixtures into the equations based upon the Leslie-Ericksen theory. The VA mode was confirmed to be superior to the IPS mode from this aspect due to the difference of the Frank elastic constants for bend and twist. Further superiority was shown quantitatively because of the contribution of the back-flow effect in the VA mode. These results were supported by referring to the molecular theory of the physical properties of LC substances.

Density functional method is applied for strongly correlated systems. Based on the assumption that the systems are composed of electrons in singly-occupied orbitals and those in doubly-occupied orbitals, a set of self-consistent equations are obtained by standard variation procedure. The equations consist of two parts. One part is to solve the wave functions of the electrons in singly-occupied orbitals and the other is to solve the wave functions of the electrons in doubly-occupied orbitals. The physical meanings of the terms aspearing in the equations are discussed. ∗Supported by the Major State Basic Research Development Program of China (Grant No. G2000067101)

Structure and bonding in the binuclear complex 1, the metallacyclocumulene, 2 and the metal–acetylene complex, 3, are studied using Density Functional Theory. The C–C bond lengths in metal–acetylene complex mainly depend on the diffuseness of the orbitals of the metal atom. Since the C1–C2–C3 angle in 2 changes to give effective overlap as the size of the metal is changed, the central C–C bond length of the cumulene remains nearly constant. In many ways the ML2 fragments determine that the bond angles C1–C2–C3 and C4–C3–C2 and the distance C2–C3 to have effective overlap with the C4H2 frame. Four in-plane delocalized molecular orbitals and two π molecular orbitals perpendicular to the MC4M′ plane contribute to the stability of the planar tetra coordination around the two central carbon atoms. At the B3LYP/LANL2DZ levels, the stability of the complex, 1, increases with decrease in the size of the M′.

In low-dimensional molecular crystals exhibiting the Peierls instability, intercolumnar interactions play an important role in electrical conduction. In this work, we propose an efficient method based on molecular orbital theory for studying the Peierls instability in molecular crystals composed of mixed-valence complexes. A perturbational approach to general N-merized systems is incorporated and applied to tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ) crystals. From the results of the calculations, a mixed state of several commensurate distortions is proposed as another aspect of the incommensurate distortion in TTF-TCNQ under atmospheric pressure, and TTF+0.5–TCNQ−0.5 crystal is found to be expected as an electronic conductor under high pressure.

We have formulated a combining rule for solid–liquid adhesion and intermolecular potentials using macroscopic adhesion data. The combining rule is applied successfully to determine macroscopic solid–liquid adhesion and to calculate adhesion patterns using molecular theory. We found that the results determined from our combining rule are better than those by the 9:3, Steele's, and 12:6 combining rules in terms of scatters and details. Our results suggest that macroscopic data from careful contact angle and adhesion findings can be used to infer relationships of unlike solid–fluid interactions at a molecular level.

Based on the ab initio molecular orbital theory at the HF/6-31G(d) level, the effect of hydration on the reduced partition function ratio (RPFR) of the boric acid molecule (B(OH)3) was evaluated in order to better understand boron isotope fractionation observed in aqueous systems. The B(OH)3(H2O) n species with n up to 12 were considered and their geometry optimization and RPFR calculations were carried out. It was induced that hydration decreased the RPFR of B(OH)3 and the degree of decrease in ln(RPFR) was ca. 1.5%, which was nearly equivalent to that of B(OH)4 -.

The nematic-isotropic phase transitions in mixtures of rod-like and disc-like molecules are studied by a mean field theory. We consider both attraction and hard-core repulsion for the model molecules, thermotropic phase transitions are found from the isotropic to one of the two types of uniaxially symmetric nematic phases: optically positive N+ and negative N−. On the other hand, biaxially symmetric nematic phase is shown to be always less stable than the uniaxial phase. We predict that re-entrant phase transition occur for the lyotropic system.