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A new stable transition-metal trihydride (ScH3) molecular nanowire was recently reported by Li et al. [J. Am. Chem. Soc. 139, 6290–6293 (2017)]. Of the two typical structures (T–ScH3 and O–ScH3), T–ScH3 is more stable than O–ScH3. However, the reason why O–ScH3 is less stable than T–ScH3 was not known. Using Perdew–Burke–Ernzerhof (PBE), PBE+U, SCAN, and HSE06, as well as crystal orbital Hamilton populations (COHPs), we investigate the orbital-projected band structures and chemical bonding of T–ScH3 and O–ScH3. It is found that the energies calculated by PBE, SCAN, and HSE06 indeed reveal that T–ScH3 is more stable than O–ScH3, and there is no occupied antibonding state at the Fermi level of the COHP curves of T–ScH3, supporting the stable Sc–H bonding of T–ScH3. To the contrary, the Sc–H bonding of O–ScH3 is unstable because there exist occupied antibonding states at the Fermi level of the COHP curves of O–ScH3. We found that the results of PBE+U are consistent with those of PBE, SCAN, and HSE06 in the case of U < Uc. However, when U > Uc, the results of PBE+U are opposite to those of PBE, SCAN, and HSE06. [ABSTRACT FROM AUTHOR]

Various levels of ab initio theory using various basis sets have been tested for the energy, structure, and harmonic vibrational frequencies of the water monomer. The level of the single, double, and perturbative triple excitation coupled-cluster method [CCSD(T)] using a large basis set (O:13s,8p,4d,2f/ H:8s,4p,2d) reproduced the experimental harmonic vibrational frequencies of the water monomer within the error of 0.6 cm-1. Other calculational methods seem to have inherent errors in predicting vibrational frequencies. Even with the above large basis set significant differences between symmetric and asymmetric stretching frequencies were found at various levels of calculational method including the commonly used Möller–Plesset 2nd (MP2) and 4th (MP4) order perturbation theories. The harmonic vibrational frequencies and force constants of the water dimer at various levels of ab initio theory have also been studied, and their shifts in the dimer relative to the monomer are discussed. At the Hartree–Fock (HF) level frequency shifts in the dimer relative to the monomer as well as hydrogen bonding strength in the dimer are underestimated, while at the MP2 level these are overestimated. The values at the CCSD(T) level seem to be reliable. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The water hexamer is known to have a number of isoenergetic structures. The first experimental identification of the O-H stretching vibrational spectra of the water hexamer was done in the presence of benzene. It was followed by the identification of the pure water hexamer structure by vibration-rotational tunneling (VRT) spectroscopy. Although both experiments seem to have located only the Cage structure, the structure of the benzene-water hexamer complex is not clearly known, and the effect of benzene in the water hexamer is unclear. In particular, it is not obvious how the energy difference between nearly isoenergetic water hexamer conformers changes in the presence of benzene. Thus, we have compared the benzene complexes with four low-lying isoenergetic water hexamers, Ring, Book, Cage, and Prism structures, using ab initio calculations. We also investigated the effects of the presence of benzene on the structures, harmonic vibrational frequencies, and infrared (IR) intensities for the four low-lying energy conformers. There is little change in the structure of the water hexamer upon its interaction with the benzene molecule. Hence the deformation energies are very small. The dominant contribution to the benzene-water cluster interaction mainly comes from the π-H interactions between benzene and a single water molecule. As a result of this π-H interaction, O-H[sub π] bond length increases and the corresponding stretching vibrational frequencies are redshifted. The IR spectral features of both (H[sub 2]O)[sub 6] and benzene-(H[sub 2]O)[sub 6] are quite similar. From both the energetics and the comparison of calculated and experimental spectra of the benzene-(H[sub 2]O)[sub 6], the water structure in these complexes is found to have the Cage form. In particular, among the four different Cage structures, only one conformer matches the experimental O-H vibrational frequencies. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electronic and vibrational hyperpolarizabilities of polyenes NH[sub 2]-(HC==CH)[sub n]-NO[sub 2] and polyynes NH[sub 2]-(C=C)[sub n]-NO[sub 2] have been investigated. As the chain length increases, the first hyperpolarizabilities increase drastically for polyenes, while they increase moderately for polyynes. Furthermore, in polyenes the vibrational first hyperpolarizabilities are almost the same as the electronic first hyperpolarizabilities, while in polyynes the former is much smaller than the latter. An analysis of the electron densities of HOMOs of polyenes and polyynes confirms that the polyene π-frame is more efficient for long pathways of nonlinear optical molecules, while the polyyne π-frame is slightly better for very short pathways. In both polyenes and polyynes, the IR intensities arise mainly from the terminal carbon sites, while the Raman intensities, from the central carbon sites. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Analogous to conventional carbon nanotubes, single-walled, chiral, γ-graphyne nanotubes (C-γGyNTs) are modeled based on the synthesized 2D γ-graphyne motif, and their electronic properties are investigated via density-functional tight-binding calculations for the first time. The resulting γGyNTs are predicted to be excellent semiconductors with moderate bandgaps ranging from 1.291 eV to 1.928 eV. In addition, the bandgaps of zigzag γGyNTs and armchair γGyNTs show damped oscillatory behaviour, while those of C-γGyNTs do not show any chirality- or diameter-dependent oscillatory behaviour. Interestingly, it is revealed that the (2a, m)-γGyNTs, where a is a positive integer, have nearly identical bandgap values, which provides a fresh method of bandgap manipulation for semiconductor devices that has not yet been reported. [ABSTRACT FROM AUTHOR]

The bias-polarity dependent multimode threshold and bipolar resistive switching characteristics in bi-layered Pt-Fe2O3 core-shell and γ-Fe2O3 nanoparticles assembly were investigated. The Ti/Pt-Fe2O3-core-shell-nanoparticles (∼20 nm)/γ-Fe2O3-nanoparticles (∼40 nm)/Pt structure exhibited a threshold switching upon applying -V at Ti electrode. However, the filaments were formed at +V and subsequently ruptured at -V, featured to be bipolar switching. After rupturing filaments, it returned to threshold switching mode. The presence of core-shell nanoparticles facilitates the threshold switching either by temporary formation of filaments or enhanced charge transport. Also, the oxygen reservoir role of Ti electrode was essential to form stable filaments for bipolar switching. [ABSTRACT FROM AUTHOR]

In an effort to examine the intricacies of electronic nanodevices, we present an atomistic description of the electronic transport properties of an isolated benzene molecule. We have carried out ab initio calculations to understand the modulation of the molecular orbitals (MOs) and their energy spectra under the external electric field, and conducting behavior of the benzene molecule. Our study shows that with an increase in the applied electric field, the energy of the third lowest unoccupied molecular orbital (LUMO) of benzene decreases, while the first and second LUMO energies are not affected. Above a certain threshold of the external electric field, the third LUMO is lowered below the original LUMO and becomes the real LUMO. Since the transport through a molecule is to a large extent mediated by the molecular orbitals, the change in MOs can lead to a dramatic increase in the current passing through the benzene molecule. Thus, in the course of this study, we show that the modulation of the molecular orbitals in the presence of a tuning parameter(s) such as the external electric field can play important roles in the operation of molecular devices. We believe that this understanding would be helpful in the design of electronic nanodevices. [ABSTRACT FROM AUTHOR]

The global minimum energy structures of the water hexamer predicted by widely used analytic water potentials are very different from each other, while the cyclic hexamer does not appear to be a low-lying energy structure. However, high levels of ab initio calculation predict that a number of low-lying energy conformers including the cyclic conformer are almost all isoenergetic due to the balance of two-body and nonadditive interactions. For modeling of water potentials, we suggest that the binding energy of the dimer be between -5.0 and -4.7 kcal (mol dimer)-1, while the three-body corrections be taken into account to a large extent. [ABSTRACT FROM AUTHOR]

A number of experimental and theoretical studies have been carried out on the anionic water hexamer in the last decade. However, none of these studies have reported the adiabatic electron detachment energy. The present study employing extensive high-level ab initio calculations report the adiabatic electron detachment energy, which explains the unusual stability of the anionic water hexamer. This stability can be correlated to the unusually intense peak observed in the photoelectron-detachment spectra. It is also shown that our previously predicted pyramid structure reproduces the important characteristics of the experimental O-H vibrational spectra. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The correlation of various properties of water clusters (H[sub 2]O)[sub n=1-10] to the cluster size has been investigated using extensive ab initio calculations. Since the transition from two dimensional (2-D) (from the dimer to pentamer) to 3-D structures (for clusters larger than the hexamer) is reflected in the hexamer region, the hexamer can exist in a number of isoenergetic conformers. The wide-ranging zero-point vibrational effects of the water clusters having dangling H atoms on the conformational stability by the O-H flapping or proton tunneling through a small barrier (∼0.5 kcal/mol) between two different orientations of each dangling H atom are not large (∼0.1) kcal/mol). Large dipole moments (>2.5 D) are found in the dimer and decamer, and significant dipole moments (∼2 D) are observed in the monomer, hexamer, and nonamer. The polarization per unit monomer rapidly increases with an increasing size of the cluster. However, this increase tapers down beyond the tetramer. The O-H vibrational frequencies serve as sensitive indicators of the status of proton donation ("d") and acceptance ("a") (i.e., the structural signature of H-bond type) for each water monomer in the cluster. In general, the magnitudes of the O-H frequencies (ν) for each cluster can be arranged in the following order: ν[sub 3][sup da] (single donor-single acceptor) ≅ν[sub 3][sup daa] (single donor-double acceptor) >ν[sub 3][sup dda] (double donor-single acceptor) >ν[sub 1][sup dda]>ν[sub 1][sup da]> (or ≅) ν[sub 1][sup daa]. The increase in the cluster size has a pronounced effect on the decrease of the lower frequencies. However, there are small changes in the higher frequencies (ν[sub 3][sup da] and ν[sub 3][sup daa]). The intensities of ν[sub 1][sup daa] and ν[sub 1][sup da] are very high, since the increased atomic charges can be correlated to the enhanced H-bond relay effect. On the other hand, the intensities of the ν[... [ABSTRACT FROM AUTHOR]

HOSO[sub 2] radical is the key intermediate for the oxidation SO[sub 2] to SO[sub 3] by OH radical in the atmosphere. The structural aspects and the energetics of the reaction HOSO[sub 2]+O[sub 2]→SO[sub 3]+HO[sub 2] have been studied using Mo\ller-Plesset (MP2) and density functional (DFT) techniques with 6-31G[sup **] and triple-ζ, quadruple-ζ, and quintuple-ζ quality basis sets including diffuse basis functions. The detailed theoretical analyses have further revealed that this reaction could proceed through the formation of intermediate complexes and an intramolecular proton transfer like transition state. The energetics of these intermediate reactions has been studied in detail. The use of MP2 methods to study such radical mechanisms had some characteristic symmetry-breaking problem with larger basis sets. This unphysical situation with larger basis set MP2 calculations in this hypervalent system has been explained through the interpretation of the relevant energy surface. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]