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In this letter, a possible reason behind selective host-guest organization in the initial stage of sI methane hydrate nucleation is provided, through density functional theory based calculations. In doing so, we have connected earlier experimental and theoretical observations on the structure and energetics of sI methane hydrate to our findings. Geometry and relative stability of small (H 2 O) 5 and (H 2 O) 6 clusters, presence of CH 4 guest, integrity and cavity radius of (H 2 O) 20 and (H 2 O) 24 , as well as the weak van der Waals type of forces, particularly dispersion interaction, are major factors responsible for initial formation of methane encapsulated dodecahedron cavity over tetrakaidecahedron.

The activation of allene by a five-membered P/B frustrated Lewis pair (FLP) has been explored by DFT based computational study. It reveals the addition of allene to the FLP takes place via two thermodynamically favorable path. But, the attack of the P center of the FLP to the middle carbon of allene is kinetically more preferable. The reaction is further analysed by taking methyl-allene and cyano-allene and which produce four thermodynamically favorable regioisomers. However the attack of the P center of the FLP to the middle carbon is kinetically more preferable. The mechanism of the reactions are carefully analysed.

Superalkalis have lower ionization energy than that of alkali atoms and superhalogens have higher electron affinity than that of halogen atoms. This property can be exploited to improve the efficacy of redox reactions that are routinely used in the scientific and industrial laboratories. Some of these reactions are theoretically studied and their thermodynamic parameters are analyzed. Alternatives to these reactions with the use of superalkalis and superhalogens are suggested by assuming similar behavior to that of their alkali metal or halogen analogues. Consequently, these reactions are analyzed, and their properties are compared to the existing reactions. Particularly, the change in reaction enthalpy, Gibbs free energy and their electrochemical potential are compared. Quantification of the reducing property of the superalkalis is also studied in the present situation by using an ionic equation. In all the cases, the results are promising and consequently, some of their applications are contemplated.

Metal aromaticity is a relatively new finding in the literature. In this work, we examine the models built with one of its simplest examples, viz. tri-aluminum cluster, through atomic probes and analyze with information-theoretic approach (ITA). Our results show that probe atoms are able to switch between aromaticity and antiaromaticity, different spin states exhibit vastly different aromaticity behaviors, and strong linear relationships can be obtained between electronic properties and ITA quantities such as Shannon entropy, Ghosh-Berkowitz-Parr entropy and information gain. These results deepen our understanding about metal aromaticity and pave a route towards investigating this phenomenon from a new perspective.

Confinement induced binding interaction patterns for noble gas atoms (Hen/m, Arn, Krn; n = 2, m = 3) atoms inside pristine and -BN doped (3, 3) single walled carbon nanotube (SWCNT) have been studied through density functional theory calculations. The kinetic stability for He dimer and trimer has been investigated at 100 K and 300 K through an ab initio molecular dynamics simulation. The positive role of doping in SWCNT in enhancing the nature of interaction as well as the kinetic stability of the said systems has been found.

Density functional theory calculations are performed to assess the influence of confinement on the strength of H···F hydrogen bond in (HF)2@Cn (n = 60, 70, 80, 90). The (HF)2 entrapping process into C60 cage is thermodynamically unfavorable whereas it is favorable in other cages. The hydrogen bond is shorter in confined cages than that in free dimer. The interaction energy between two HF units is maximum in C80 whereas the bond is the shortest in C70. It appears that in confined situation a shorter bond does not necessarily mean a stronger bond. Energy decomposition analysis and electron density analysis are performed to explain the results.

Inspired by carbo-benzene, we have analyzed in silico the stability of carbo-borazine (C12B3N3H6) and the iminobora-mer of borazine (B9N9H6). Both systems may be regarded as the inorganic analogues of carbo-benzene, being B9N9H6 the perfect case. Unlike aromatic carbo-benzene, C12B3N3H6 and B9N9H6 can be classified as almost nonaromatic systems as indicated by the computed induced magnetic field. All these systems undergo dimerization very readily; therefore, they cannot be synthesized as such. However, akin to substituted carbo-benzene, the substitution of the hydrogen atom of C12B3N3H6 and B9N9H6 by other groups could stabilize them.

An ab initio molecular dynamics study on Ng 2 @C 60 (Ng = He Kr) systems is performed to analyze the movement of Ng 2 molecules inside a C 60 cage. Within 500 fs time window, the He 2 undergoes precession encompassing translation, vibration and rotation readily whereas other Ng 2 molecules show usual vibration but the degrees of translation and rotation decrease with an increase in size of the Ng atoms. Increase in interaction between the Ng centers and cage carbons and an increased distortion of cage in moving from He to Kr seem to be responsible for this. During the movement, the Ng 2 units behave as single entity.

Prompted by a recent Letter (Brito et al., 2013) [9], stability and dynamics of the cyclic and linear Be 3 2 - clusters are studied. CASSCF is used over coupled cluster and other single reference methods on the basis of T1 diagnostic. Ab initio molecular dynamics (ADMP) study reveals the fate of cyclic and linear Be 3 2 - clusters up to 3.25 ps. Total energy and conceptual density functional theory based reactivity descriptors, hardness and electrophilicity vary with time during simulation. Energy, hardness and electrophilicity trajectories help to understand the structural dynamics of Be 3 2 - clusters.

A computational study is carried out to simulate methane hydrates as well as to know the effect of HF doping on their stability and structure. By using ab initio molecular dynamics simulation interaction of methane with HF doped clathrate hydrates is studied. The total energy profiles present insights into the stability and structure of methane hydrates. The HF doping increases the stability of the methane hydrates without any distortion of the cage when methane is encapsulated in 5 12 cages.

Theoretical investigation on planar N 6 4 - and N 4 2 - rings has been performed. The aromaticity of the rings has been analyzed through their nucleus independent chemical shift (NICS) values as well as the σ- and π-contribution of the Z-component of the induced magnetic field. Counter to a previously reported result [Chem. Phys. Lett. 432 (2006) 331], the N 6 4 - ring is found to be a local minimum and aromatic with planar D6h symmetry. The N 4 2 - ring exhibits conflicting aromaticity like Al 4 4 - . Both the N 6 4 - and N 4 2 - rings can be stabilized in presence of suitable counter cations and systems like N6Ca2 and N4Li2 can trap molecular hydrogen.

A two-step substitution reaction: CpZnZnCp ( D 5 h ) → - 2 Cp - + 2 Be 3 2 - [ Be 3 ZnZnBe 3 ] 2 - ( D 3 h ) → - 2 Zn + + 2 Be + [ Be 3 BeBeBe 3 ] 2 - ( D 3 h ) is studied at the B3LYP/6-311+G[d] level of theory. The resulting all-beryllium sandwich-like complex, Be 8 2 - is highly stable and aromatic. The ring-Be atoms show different reactivity towards hard and soft electro (nucleo) philes than the bond-Be atoms.

In the light of the generalized philicity concept, intermolecular reactivity of some selected systems is analyzed and the concept of group philicity (ωg) has been proposed. It can be found that DFT offers the possibility to calculate important functional group properties from the first principles in a non-empirical way. Unified philicity clearly predicts the exact reactivity trends for all the selected systems. In conjunction with the electrophilicity, ω g + offers direct availability of charge distributions of molecular systems in a more pronounced way than the relative electrophilicity/nucleophilicity and the group softness and might be of importance in reactivity studies.

Condensed Fukui functions (FF) and philicity provide vital information about functionally reactive sites in molecules. The effect of solvation on the condensed FF and philicity has been assessed by computing these local quantities in both gas and solvent media. The various population schemes used to calculate condensed quantities have several limitations viz., computational time, multiplicity problem and interpretation of negative values. To overcome this we used the direct method to evaluate the condensed quantities in both gas and solvent media. Hirshfeld population scheme has also been employed to avoid negative FF values. The implications of the results are discussed.

We present a comprehensive study of electric field effects on the global and local chemical reactivity indices. We use the effect of an applied uniform electric field on chosen molecules and stockholder population scheme to derive the local reactivity profiles. We find that the changes in the pattern of reactivity indices are strongly influenced when the electric field is applied to the system, this effect being more noticeable as the number of atoms in the molecule increases as well as the strength of the applied field. The field-induced polarization leads to changes in the global and local reactivity descriptors.

Softness, polarizability and mean excitation energy are calculated for several atoms confined in a spherical box, using numerical Hartree-Fock technique with a Dirichlet boundary condition. Both softness and polarizability increase and mean excitation energy decreases and ultimately level off when the size of the box increases. In general softness and polarizability decrease along a period and increase along a group of the periodic table. Softness varies linearly with the cuberoot of polarizability for all the confined systems. Energy, virial and various moments follow the expected trends.

The possibility of gaining insight into chemical bonding and reactivity through various local temperatures and associated entropy densities is explored. Comparisons of these quantities with other local reactivity descriptors like the electron density, the Laplacian of the density, the Fukui function and the electron localization function are made. The water molecule has been chosen as a prototype for analyzing the above-mentioned quantities. The global entropies are also calculated for the atoms He to Ne. Most of the local quantities preserve the molecular symmetry and some are well suited for use as reactivity indices.

The maximum hardness principle is examined within the Gyftopoulos-Hatsopoulos three-level model for an electronic system. As an atom or a molecule approaches equilibrium at some chemical potential μ and constant temperature T, its softness (inverse hardness) is shown to most often approach a minimum value.

Temporal evolution of local and global hardness during a chemical reaction modelled as a collision process between a nitrogen atom and a proton has been studied within a quantum fluid density functional framework. Variation of local hardness is similar to that of charge density. Time dependence of global hardness seems to be governed by a dynamic variant of the maximum hardness principle.

Ab initio SCF calculations using the 6-31G** basis set have been performed on a number of molecules in order to test the validity of maximum hardness and maximum molecular valency principles. It has been observed that the former is valid under a variety of bonding situations, while the latter breaks down in the case of highly ionic molecules.

A comparative study has been made in order to monitor the scattering of a particle from different model surfaces having maximum dimension one. Although the differential cross-section plots exhibit marked differences, the self-similar behaviour has been manifested in the integrated cross-section data through their power-law dependence on the incoming wave-vector.

Using a recently proposed kinetic energy density functional and an amalgamation of density functional theory with quantum fluid dynamics, a time-dependent Kohn-Sham-type equation in three-dimensional space, which is a new non-linear Schrodinger equation, has been derived. The equation is also derived through the stochastic interpretation of quantum mechanics. A molecular “thermodynamic” viewpoint is suggested in terms of space-time-dependent quantities. Numerical solution of the above equation yields the time-dependent charge density, current density, effective potential and chemical potential. Perspective plots of these quantities for the proton-neon 25 keV head-on collision are presented.

Two simple uncertainty corrections to the Thomas-Fermi theory are suggested. The first is derived according to statistical-mechanical considerations, and the second is obtained by a semi-empirical extension to many-electron systems of a spherical one-electron-system result. For both corrections results are quite good; in particular, most of the results from the second correction are probably the best reported so far.

A new simple form for the atomic kinetic energy-density functional ( t ) is proposed as a sum of the Thomas-Fermi term and a radial correction term, namely, t [ p ] = (3/10) (3π 2 ) 2/3 p 5/3 - ( 1/40 )( r ·▽ p )/ r 2 , where the first term is the Thomas-Fermi term and p ( r ) is the Hartree-Fock atomic density. The correction term is part of the -(1/4)▽ 2 p term which occurs in the kinetic energy density; it adds mainly terms of O( Z 2 ) and O( Z 5/3 ) to the Z 7/3 atomic Thomas-Fermi energy. The above form generally displays improved local and global behaviour for atomic kinetic energies. Besides satisfying the virial theorem, it gives rise to chemical binding in molecules.

The Euler-Lagrange equation in density functional theory is generally a differential (or integro-differential) equation. An integral equation for direct calculations has been obtained from the Euler-Lagrange equation. It is easier to solve the new equation numerically than the original differential equation.