An augmented effective core potential basis set for the calculation of molecular polarizabilities

Calculations of molecular polarizabilities require basis sets capable of accurately describing the responses of the electrons to an external perturbation. Unfortunately, basis sets that yield suitable quantitative results have traditionally been all-electron sets with large numbers of primitives, making their use computationally intractable even for moderately sized systems. We present a systematic augmentation of the effective core potential basis set of Stevens et al. [J Chem Phys 81, 12 (1984), Can J Chem 70, 612 (1992)] for 39 main group elements based on the procedure used to construct diffuse and polarization functions in the well-known Sadlej basis sets [Collec Czech Chem Comm 53, 1995 (1988)]. Representative calculations have been performed and we have shown that results to within 1% of all-electron calculations using the Sadlej basis set can be obtained for <1-35% of the computational cost using this new basis set.     

On the Phase Diagram of LiF-KCI-KBr and KF-NaCI-NaBr Systems

The phase diagrams of LiF-KCl-KBr and KF-NaCl-NaBr systems have been de'er-mined by visual polythermal method with the X-ray diffraction analysis of solid phases.The thermodynamical behaviour of the molten salt solutions of these systems are estimated on the basis of the data of phase diagrams.The thermodynamical behaviour of these recipioral-salt-pair containing systems is explained by the results of the computerized simulation using Monte Carlo method.     

Calculation of properties of ternary liquid mixtures on the basis of properties of binary solutions

Various methods of calculating properties of ternary systems using the properties of binary solutions have been analyzed on the basis of experimental and published data.     

A study by Raman spectroscopy and the semiempirical AM1 method on several 1,2-dihydroxybenzene solutions

The Raman spectra of 1,2-dihydroxybenzene (catechol) dissolved in six different compounds have been obtained and, on the basis of frequencies and depolarization ratios, the relevant structure of the solute has been inferred in every case. In addition, rotational barrier calculations using the AMI semiempirical method have been performed on several catechol—solvent systems. The theoretical results were in accord with experimental data and were related to structural properties of the solvents.     

FSGO calculation of harmonic force fields of selected polyatomic hydrides

Harmonic force fields for several polyatomic hydrides of first-row atoms have been determined using the FSGO method and its extensions. The obtained results suggest that for larger polyatomic systems, the use of small, but completely optimised basis sets composed mainly of bond functions may be more economical than the conventional large basis set LCAO approach.     

Valence-bond calculations on ZNO and HGO using integrals computed through the semiempirical AM1 method

Valence-bond calculations have been carried out on ZnO and HgO using a basis set of Slatertype atomic orbitals and the one- and two-electron integrals as computed in the semiempirical AM 1 molecular orbital method. The zero differential overlap approximation has been used to calculate integrals between atomic orbital Slater determinants using the rules for matrix elements between determinants formed by orthogonal orbitals. Diabatic and adiabatic curves have been analyzed for the two systems, and results compared with molecular orbital AM 1 results. © 1992 John Wiley & Sons, Inc.     

Calculation of the interaction energy in a localized representation for a trimer (Ne3) system

We studied the transferability of the localized orbitals (LOs) of interacting Ne atoms using several basis sets. Both at SCF and at MP2 and MP3 levels, the contributions of the LOs have been calculated and discussed for the Ne₂ and Ne₃ systems. It was shown that for the LOs the transferability is satisfied to a good extent and due to the transferability the interaction energy at the correlated level can be calculated by using only the LOs of the supermolecule. The basis set superposition error (BSSE) is simply extracted from the intramolecular parts of the correlation energy. The two- and three-body interaction energies have been investigated for the studied systems. © John Wiley & Sons, Inc.     

The Challenge of ab Initio Calculations in Small Neon Clusters

Weakly bound neon dimer, trimer and tetramers are studied at HF and CCSD(T) levels using Dunning, ANO and SIGMA-s basis sets. Their ground-state binding energies are studied along with some structural properties. SIGMA-s basis sets have been developed explicitly for this issue but in a manner that can be readily applied to other atoms for the study of larger weakly bound systems. The difficulties for attaining accurate results on these systems are assessed by the computation of total, atomization and correlation energies, as well as equilibrium distances, with several basis sets of increasing size, ranging from non-augmented to double-augmented versions. Extrapolations are proposed to predict stabilization energies and the results are compared with previously published data.     

EPR studies of reduced Zn-chlorins and their isotope substituted analogues

Radical anions of Zn-chlorin, Zn-octaethylchlorin complexes and their ¹⁵N and deuterium substituted analogues have been studied by EPR spectroscopy and the INDO molecular orbital method in the unrestricted Hartree-Fock procedure. Parameters of experimental spectra, determined by using the iterative least-squares fitting method, have been compared with those calculated on the basis of spin density distribution. A satisfactory agreement between the experimental hyperfine coupling constants and theoretical ones for the systems studied has been obtained.     

The use of MIDI basis set at the correlated level

The H₂O + H₂O, the NH₃ + NH₃, the BH₃ + H₂O and the Ne + Ne systems have been studied in the supermolecule approach, using several medium sized basis sets (especially the so-called MIDI basis set). The calculations have been carried out by the use of localized molecular orbitals (LMOs).

The dispersion interaction energies have been computed by a new method (Kozmutza and Kapuy; Int. J. Quantum Chem., 38 (1990) 665), whose essence lies in the use of LMO contributions at the correlated level.

The method proposed seems to be useful for the H₂O + H₂O, the NH₃ + NH₃, and the Ne + Ne systems at different intermolecular distances, using the MIDI basis, but fails in describing correctly the correlation energy for the BH₃ + H₂O system.     

儿茶素-胞嘧啶分子间相互作用的密度泛函研究

采用密度泛函理论的B3LYP方法,在6-31+G*基组水平上研究了儿茶素-胞嘧啶分子间相互作用机制,得到稳定的儿茶素-胞嘧啶复合物11个.计算结果表明氢键对于复合物的稳定性起着重要的作用,并且当复合物形成2个或更多的氢键时,氢键的类型及强度共同决定着复合物的稳定性.我们还应用了分子中的原子(AIM)理论和自然键轨道(NBO)理论对这11种复合物中氢键的性质和特征进行了分析.通过研究发现,所有的氢键复合物进行基组重叠误差(BSSE)校正后的相互作用能为-17.35～-43.27kJ/mol,相互作用能主要由氢键所贡献.振动分析显示,氢键的形成使相对应键的对称伸缩振动频率减小,说明这些复合物中形成的氢键都是正常的红移型氢键,与实验结果相一致.     

Density functional theory study on the interaction of catechin and cytosine

The interacting patterns and mechanism of the catechin and cytosine have been investigated using the density functional theory B3LYP method with 6-31+G* basis set.Eleven stable structures of the catechin-cytosine complexes have been found respectively.The results indicate that the complexes are mainly stabilized by the hydrogen bonding interactions.Theories of atoms in molecules(AIM) and natural bond orbital(NBO) have been utilized to investigate the hydrogen bonds involved in all the systems.The interactio...     

Are donor–acceptor self organised aromatic systems NLO (non-linear optical) active?

This contribution to the understanding of non-linear optical (NLO) properties of organic systems is concentrated on donor–acceptor aromatic systems such as [2]catenanes. We report accurate ab initio quantum chemical calculations of the first static hyperpolarizability (β) of donor–acceptor aromatic systems containing naphthalene and anthracene as electron donors and pyromellitimide and naphthadiimide as electron acceptors. We investigate the NLO effect when the donor acceptor units are not connected through a bridge. In this kind of system the electronic communication between donor and acceptor is solely due to through space charge transfer mechanism. Geometries of all molecular systems were optimised at the Hartree–Fock level with STO-3G minimal basis set and with the 3-21G split valence basis and finally with 6-31G basis set using GAUSSIAN 98W. The first static hyperpolarizabilities of these molecular systems were calculated using Hartree–Fock level using 6-31G basis set using GAUSSIAN 98W. To understand the possibility of developing these systems as NLO materials we have also calculated the linear and nonlinear optical properties of bridged donor–acceptor systems. The study suggested that these unconnected donor–acceptor systems equivalent to some [2]catenanes reported in literature in general have little influence on the first static hyperpolarizability, however, the linked macro cyclic systems may have potential applications in the development of non-linear optical materials.     

Advanced detector systems: What do they have to offer for activation analysis?

Neutron activated reference materials have been analyzed using a standard Ge(Li)-detector with 17% relative efficiency, a very large Ge-detector with 96% relative efficiency, and a well-type Ge detector. Sensitivities are presented, and usefulness of these systems for NAA is compared on the basis of performance, economics and complexity.     

Analysis of pair interaction in a bipolar mesogen 4‐(4‐hydroxylbutyloxy)‐4′‐cyano‐biphenyl: A comparative study based on semiempirical and DFT methods

Structure of 4‐(4‐hydroxylbutyloxy)‐4′‐cyano‐biphenyl (H4CBP) molecule has been optimized using density functional B3LYP with 6‐31G (d) basis set taking crystallographic geometry as input. Using the optimized geometry, electronic structure of the H4CBP molecule has been evaluated on the basis of semiempirical methods and DFT calculations. Intermolecular interaction energy between a pair of H4CBP molecules has been evaluated by using Rayleigh–Schrodinger perturbation theory modified with multicentered multipole expansion method for the electrostatic part while dispersion and repulsion terms have been calculated using Kitaigorodskii formula. The results obtained through semiempirical and DFT calculations have been compared for various interacting conditions, viz.: (a) stacking, (b) in‐plane, and (c) terminal interactions. A comparative analysis of the results has been carried out with a view to examine suitability of different methods to study molecular aggregations in moderately large organic systems. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Ab initio calculations of electrostatic potentials and deformation densities for a series of choline ester model systems

Ab initio LCAO-MO-SCF calculations using a double zeta basis set have been performed for the methyl esters of acetic acid, carbamic acid, methylcarbonic acid, and trifluoracetic acid, in order to model the corresponding choline esters. The systems have been compared by means of population analyses, electron density differences, electrostatic potentials and potential differences. The significance of the electrostatic potential in connection with crystal structure and packing has been studied. The differences in the proton affinity of the compounds have been correlated to differences in the potentials.     

Settling-time dependence of rat bone marrow cell partition and counter-current distribution in charge-sensitive aqueous two-phase systems. Relationship with the cell partitioning mechanism.

Differences in the settling-time dependence of single and multiple cell partitions have been found between heterogeneous (bone marrow cells) and homogeneous (erythrocytes) populations when using charge-sensitive dextran-poly(ethylene glycol) aqueous two-phase systems. The cell populations were partitioned using both single test-tube experiments and multiple thin-layer counter-current distribution. Lengthening the settling time, to favour phase separation, and decreasing the upper phase volume are more effective in fractionation by the counter-current distribution of heterogeneous cell populations than increasing the interfacial tension, although all three were employed to speed phase settling. On the basis of these results, the original cell partitioning mechanism proposed for non-charge-sensitive systems has been extended to charge-sensitive systems.     

Strained delocalized carbenoid ring systems — A theoretical investigation

A number of ring compounds containing a divalent carbon center (carbenes) have been studied usingab initio quantum chemical methods. The studied systems include: imidazol-2-ylidene, 4-pyranylidene, 9-xanthylidene, cyclohexa-2,5-dienylidene and 4-oxocyclohexa-2,5-dienylidene. Extended ANO type basis sets were used. Wave functions and energies were obtained with a multiconfigurational approach (CASSCF), where dynamic correlation effects are treated by using second-order perturbation theory (CASPT2).The singlet-triplet splitting has been found to depend linearly on the energy separation between the two carbene orbitals. All systems, where this splitting is larger than about 10 eV have been found to have a singlet ground state, while those with a smaller gap have a triplet ground state. A number of excited states have been characterized. Computed excitation energies are in agreement with experiment in cases where such information is available.     

The implementation of ab initio quantum chemistry calculations on transputers

Summary The RHF and geometry optimization sections of the ab initio quantum chemistry code, GAMESS, have been optimized for a network of parallel microprocessors, Inmos T800-20 transputers, using both indirect and direct SCF techniques. The results indicate great scope for implementation of such codes on small parallel computer systems, very high efficiencies having been achieved, particularly in the cases of direct SCF and geometry optimization with large basis sets.The work, although performed upon one particular parallel system, the Meiko Computing Surface, is applicable to a wide range of parallel systems with both shared and distributed memory.     

Computation of large systems with an economic basis set: systems in excited states

An economic basis set for ab initio calculations of systems in excited states has been studied. The economic basis set, in which the polarization functions are applied only to oxygen (O), while the 6-31G basis set is used for carbon (C) and hydrogen (H), is shown to save considerable computing time and to give reliable geometric and frequency measurements. In addition, the economic basis set has been considered for obtaining reliable excitation energies, with the correction factor, using high-level single-point energy calculations. This study is expected to shed light on basis set selection for computations of large systems in excited states.