Roothaan–Hartree–Fock wave functions for cations and anions in Slater-type basis sets with doubly even tempered exponents

Summary Roothaan-Hartree-Fock wave functions in Slater-type basis sets are reported for the cations Li⁺-Cs⁺ and anions H^–-I^– using the double even tempering (DET) method of selecting orbital exponents. The DET total energies do not differ from the corresponding numerical Hartree-Fock values by more than 0.2 millihartrees for the cations and anions. The present results together with the previous ones for neutral atoms [Theor Chim Acta 88:273 (1994)] provide a compilation of DET wave functions of near Hartree-Fock quality for all the neutral and singly-charged atoms with the number of electronsN54.     

Ab initio and DFT studies on vibrational spectra of some halides of group IIIB elements

The vibrational spectra of some group IIIB elements halides MX(3) and their dimmers, M(2)X(6) (M=Sc(III), Y(III), La(III); X=F, Cl, Br, I), have been systematically investigated by ab initio restricted Hartree-Fock (RHF) and density functional B3LYP methods with LanL2DZ and SDD basis sets. The optimized geometries and calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational frequencies, calculated by two methods with different basis sets, are compared to each other. The effect of the methods and the basis sets used on the calculated vibrational frequencies are discussed. Some vibrational frequencies of these complexes are also predicted.     

Kinetics and mechanism of bimolecular electron transfer reaction in quinone-amine systems in micellar solution

Photoinduced electron transfer (ET) reactions between anthraquinone derivatives and aromatic amines have been investigated in sodium dodecyl sulphate (SDS) micellar solutions. Significant static quenching of the quinone fluorescence due to high amine concentration in the micellar phase has been observed in steady-state measurements. The bimolecular rate constants for the dynamic quenching in the present systems k(q) (TR), as estimated from the time-resolved measurements, have been correlated with the free energy changes DeltaG(0) for the ET reactions. Interestingly it is seen that the k(q) (TR) vs DeltaG(0) plot displays an inversion behavior with maximum k(q) (TR) at around 0.7 eV, a trend similar to that predicted in Marcus ET theory. Like the present results, Marcus inversion in the k(q) (TR) values was also observed earlier in coumarin-amine systems in SDS and TX-100 micellar solutions, with maximum k(q) (TR) at around the same exergonicity. These results thus suggest that Marcus inversion in bimolecular ET reaction is a general phenomenon in micellar media. Present observations have been rationalized on the basis of the two-dimensional ET (2DET) theory, which seems to be more suitable for micellar ET reactions than the conventional ET theory. For the quinone-amine systems, it is interestingly seen that k(q) (TR) vs DeltaG(0) plot is somewhat wider in comparison to that of the coumarin-amine systems, even though the maxima in the k(q) (TR) vs DeltaG(0) plots appear at almost similar exergonicity for both the acceptor-donor systems. These observations have been rationalized on the basis of the differences in the reaction windows along the solvation axis, as envisaged within the framework of the 2DET theory, and arise due to the differences in the locations of the quinones and coumarin dyes in the micellar phase.     

Theoretical studies on vibrational spectra of some halides of Group IIB elements

The vibrational spectra of Group IIB elements halides MX2 and their dimers M2X4 (M=Zn(II), Cd(II) and Hg(II); X=F, Cl, Br and I) have been systematically investigated by ab initio RHF and B3LYP methods with LanL2MB, LanL2DZ and SDD basis sets. The optimized geometries, calculated vibrational frequencies are evaluated via comparison with the experimental data. The vibrational frequencies, calculated by these methods with different basis sets, are compared to each other too. The best results can be obtained by RHF/SDD method, with this method, the deviations for MX2 and Hg2X4 are <7%. Some vibrational frequencies of M2X4 that have not been experimentally reported are also predicted.     

Systematic Gaussian basis-set limit using completeness-optimized primitive sets. A case for magnetic properties

We discuss the connection between the completeness of a basis set, measured by the completeness profiles introduced by Chong (Can J Chem 1995, 73, 79) at a certain exponent interval, and the possibility of reproducing molecular properties that arise either in the region close to the atomic nuclei or in the valence region. We present a scheme for generating completeness-optimized Gaussian basis sets, in which a preselected range of exponents is covered to an arbitrary accuracy. This is done by requiring Gaussian functions, the exponents of which are selected without reference to the atomic structure, to span the range with completeness profile as close to unity as wanted with as few functions as possible. The initial exponent range can be chosen suitable for calculations of molecular energetics or other valence-like properties. By extending the exponent range, properties requiring augmentation of the basis at a given angular momentum value and/or in a given distance range from the nucleus may be straightforwardly and systematically treated. In this scheme a universal, element-independent exponent set is generated in an automated way. The relation of basis-set completeness and performance in the calculation of magnetizability, nuclear magnetic shielding, and spin-spin coupling is tested with the completeness-optimized primitive sets and literature basis sets.     

乙烯醇锂的从头算研究

用限制的HF/3-21G和HF/6-31G^*优化乙烯醇锂的几种可能构型,比较了它们的稳定性.用限制的HF/3-1G,从乙醛开始,探讨了气相反应生成乙烯醇锂的机理,并在MP2水平上用6-31G^*基组计算了反应热.     

[M(Im)2X2]型配合物的Far-IR和Raman光谱的理论研究

本文用从头计算RHF和密度泛函B3LYP方法以及LanL2DZ，SDD和6-31G(d)基组计算了配合物M(Im)₂X₂ (Im=imidazole；M=Zn(Ⅱ)，Pd(Ⅱ)，Pt(Ⅱ)；X=F，Cl，Br，I)的几何构型以及Far-IR和Raman振动频率。计算结果表明，对Zn(Ⅱ)配合物而言,B3LYP/6-31G(d)方法得到的几何参数与实验值吻合得最好，B3LYP/SDD次之。在计算Far-IR和Raman振动频率时，发现采用6-31G(d)基组，两种方法计算的结果差别不大。对LanL2DZ和SDD基组而言，对计算结果影响较大的是理论方法，基组影响甚微，个别的振动频率基组影响较大，相比较而言，SDD基组得到的结果更好一些。本文所使用的两种计算方法都能得到与实验值比较吻合的结果，而用从头计算RHF方法计算的结果与实验值更接近一些。在此基础上，预测了Pd(Ⅱ)和Pt(Ⅱ)配合物的Far-IR和Raman振动频率。     

Multilayer formulation of the fragment molecular orbital method (FMO)

The fragment molecular orbital method (FMO) has been generalized to allow for multilayer structure. Fragments are assigned to layers, and each layer can be described with a different basis set and/or level of electron correlation. Interlayer boundaries are treated in the general spirit of the FMO method since they also coincide with some interfragment boundaries. The question of the one- and two-layer FMO accuracy dependence upon the fragmentation scheme is also addressed. The new method has been applied to predict the reaction barrier and the reaction heat for the Diels-Alder reaction with a representative set of reactants based on dividing fragments in two layers. The 6-31G* basis set has been used for the active site and the 6-31G*, 6-31G, 3-21G, and STO-3G basis sets have been used for the substituents. Different levels of electron correlation (RHF, B3LYP, and MP2) have been applied to layers in systematic fashion. The one-layer FMO errors in the reaction barrier and the reaction heat were 2.0 kcal/mol or less for all levels applied (RHF, B3LYP, and MP2), relative to full ab initio methods. For the two-layer method the error was found to be several kcal/mol. Benchmark calculations of the activation barrier for the decarboxylation of phenylcyanoacetate by beta-cyclodextrin demonstrated that the two-layer calculations are efficient, being 36 times faster than the regular DFT, as well as accurate, with the error being 1.0 kcal/mol.     

Half-Projected and Projected Hartree-Fock Calculations for Singlet Ground States. i. four-Electron Atomic Systems

The half-projected Hartree-Fock function (HPHF ) for singlet states is defined as a linear combination of two Slater determinants, which contains only spin eigenfunctions with even quantum number. Using a self-consistent procedure based on the generalized Brillouin's theorem, the RHF , HPHF and PHF functions are deduced for the ground states of the Li^?, Be, B⁺, and C²⁺ systems, in a limited basis set. It is found that the HPHF function yields better energy values than the RHF function, very close to that of the PHF one. The HPHF scheme seems thus to be useful as a substitute for the PHF model, specially in the case of large electronic systems in which the latter method becomes unmanageable.     

Relativistic correlating basis sets for the sixth-period d-block atoms from Lu to Hg

Contracted Gaussian-type function sets to describe valence correlation are developed for the sixth-period d-block atoms Lu through Hg. A segmented contraction scheme is employed for their compactness and efficiency. Contraction coefficients and exponents are determined by minimizing the deviation from accurate natural orbitals generated from configuration interaction calculations, in which relativistic effects are incorporated through the third-order Douglas-Kroll approximation. The present basis sets yield more than 99% of atomic correlation energies predicted by accurate natural orbital sets of the same size. Relativistic model core potential calculations with the present correlating sets give the spectroscopic constants of the AuH molecule in excellent agreement with experimental results.     

Ab initio calculations on sulfur-containing compounds. II. One-electron properties of H2S

Closed-shell RHF one-electron properties are calculated for H₂S using a total of 41 different s, p basis sets and two polarized basis sets (6–31G* and 6–31G**). Total energies and geometries alone are not a comprehensive criteria for selecting the best basis sets. It is shown here that the comparison of a number of one-electron properties can serve as an excellent criteria for testing basis sets. The quality or reliability of a basis set is taken as being its agreement with a large uncontracted s, p basis set (s, p limit).     

Efficient model chemistries for peptides. I. General framework and a study of the heterolevel approximation in RHF and MP2 with Pople split-valence basis sets

We present an exhaustive study of more than 250 ab initio potential energy surfaces (PESs) of the model dipeptide HCO-L-Ala-NH(2). The model chemistries (MCs) investigated are constructed as homo- and heterolevels involving possibly different RHF and MP2 calculations for the geometry and the energy. The basis sets used belong to a sample of 39 representants from Pople's split-valence families, ranging from the small 3-21G to the large 6-311++G(2df,2pd). The reference PES to which the rest are compared is the MP2/6-311++G(2df,2pd) homolevel, which, as far as we are aware, is the most accurate PES in the literature. All data sets have been analyzed according to a general framework, which can be extended to other complex problems and which captures the nearness concept in the space of MCs. The great number of MCs evaluated has allowed us to significantly explore this space and show that the correlation between accuracy and computational cost of the methods is imperfect, thus justifying a systematic search for the combination of features in a MC that is optimal to deal with peptides. Regarding the particular MCs studied, the most important conclusion is that the potentially very cost-saving heterolevel approximation is a very efficient one to describe the whole PES of HCO-L-Ala-NH(2). Finally, we show that, although RHF may be used to calculate the geometry if a MP2 single-point energy calculation follows, pure RHF//RHF homolevels are not recommendable for this problem.     

Optimization of augmentation functions for correlated calculations of spin-spin coupling constants and related properties

A new hierarchy of augmented basis sets optimized for the calculation of molecular properties such as indirect spin-spin coupling constants is presented. Based on the Dunning hierarchy of cc-pVXZ (X = D, T, Q, and 5) basis sets augmentation functions with tight exponents have been optimized for coupled-cluster calculations of indirect spin-spin coupling constants. The optimal exponents for these tight functions have been obtained by optimizing the sum of the absolute values of all contributions to the coupling constant. On the basis of a series of test cases (CO, HF, N(2), F(2), H(2)O, NH(3), and CH(4)) we propose a set of tight s, p, and d functions to be added to the uncontracted Dunning basis sets, and, subsequently, to recontract. The resulting ccJ-pVXZ (X = D, T, Q, and 5) basis sets demonstrate excellent cost efficiency in benchmark calculations. These new basis sets should generally be applicable for the calculation of spin-spin coupling constants and other properties that have a strong dependence on powers of 1r or even contain a delta distribution for correlated ab initio methods.     

Conformational stability, optimized geometries, vibrational and electronic spectra of methacryloyl bromide in ground and excited electronic states

In order to understand conformational isomerism in methacryloyl bromide (MABR) in the ground (S(0)) and the first excited (S(1)) electronic states and to interpret the vibrational and electronic spectra of its conformers in the S(0) state, quantum mechanical calculations using Density Functional Theory (DFT) and RHF methods with extended basis sets 6-31G, 6-31G** and 6-311+G(d,p) have been conducted. In RHF calculations, electron correlation effects have been included at the M?ller-Plesset MP2 level. It is inferred that in both the electronic states the molecule may exist in two isomeric forms-s-trans and s-cis; the former being more stable than the later by about 1.629 kcal mol(-1) in the S(0) state and by about 2.218 kcal mol(-1) in the S(1) state. Electronic transition tends to increase the s-trans/s-cis and s-cis/s-trans, rotational barriers from 7.059 kcal mol(-1) (2468.1 cm(-1)) and 5.428 kcal mol(-1) (1897.8 cm(-1)) in S(0) state to 23.594 kcal mol(-1) (8249.4 cm(-1)) and 21.376 kcal mol(-1) (7473.9 cm(-1)) in the S(1) state. Completely optimized geometries of the two conformers in S(0) state reveal that while there is no significant difference in their bond lengths, some of the bond angles associated with COBr group are appreciably different. Electronic excitation tends to change both the bond lengths and bond angles. Based on suitably scaled DFT and RHF results obtained from the use of 6-31G** and 6-311+G(d,p) basis sets, a complete assignment is provided to the fundamental vibrational bands of both the s-trans and s-cis conformers in terms of frequency, form and intensity of vibrations and potential distribution across the symmetry coordinates in the S(0) state and a comparison has been made with experimental assignments. A theoretical prediction of the electronic transitions in the near UV-region in the two conformers and their tentative assignment has been provided on the basis of CI level calculations using 6-31G basis set.     

Comparison of the RHF,NDDO, and MOM molecular one-electron expectation values calculated using minimum basis sets with Slater,Burns, Clementi,and BLMO exponents

The effect of different exponents, Slater, Burns, Clementi, and Best Limited Molecular Orbital (BLMO ) on the approximate one-electron property expectation values from minimum basis-set calculations is reported for Roothaan–Hartree–Fock (RHF ), neglect of diatomic differential overlap (NDDO ), and maximum overlap method (MOM ) calculations on FH, CO, and LiH.     

Theoretical studies on vibrational spectra of mixed cyanide-halide complexes of platinum(IV) and palladium(IV)

The vibrational spectra of mixed cyanide-halide complexes, M(CN)4X 2 2- and M(CN)5X2- (M=Pt and Pd; X=F, Cl, Br and I), have been systematically investigated by ab initio RHF, B3LYP and MP2 methods with LanL2DZ and SDD basis sets. The calculated vibrational frequencies of platinum complexes are evaluated via comparison with the experimental values. In the infrared frequency region, the C--N stretching vibrational frequencies calculated at B3LYP level with two basis sets are in good agreement with the observed values with deviations, -16-4 cm(-1) for Pt(CN)4X 2 2- and -18 to -2 cm(-1) for Pt(CN)5X2-. However, in far-infrared region, the results obtained at RHF level are better than those calculated at B3LYP and MP2 levels. For RHF/SDD method, the deviations for Ptz.sbnd;X and Ptz.sbnd;C stretching vibrational frequencies are -14-1 and -12 to -2 cm(-1) in the complex Pt(CN)4X2 2-, -19 to -11 and -15-14 cm(-1) in the Pt(CN)5X2- complex, respectively. The vibrational frequencies of palladium(IV) and some platinum(IV) complexes that have not been experimentally reported are predicted.