Masahiro Sekiya

Contracted polarization functions for the atoms magnesium through argon

Abstract Contracted Gaussian-type function (GTF) sets are developed for polarization functions of the atoms from magnesium to argon. A segmented contraction scheme is used for its compactness and computational efficiency. The contraction coefficients and orbital exponents are determined to minimize the difference from accurate atomic natural orbitals in polarization space. The present polarization functions yield greater than 99.5% of atomic correlation energies predicted by accurate natural orbitals of the same size. Molecular tests of the polarization functions are performed for the P 2 and Si 2 molecules at self-consistent field (SCF) and single and double excitation configuration interaction (SDCI) levels. The present polarization function sets are shown to be superior to both averaged atomic natural orbital (ANO) and Dunning et al.s correlation consistent sets.

Valence and correlating basis sets for the second transition-metal atoms from Y to Cd

Contracted Gaussian-type function sets are developed for the valence 5s and 4d orbitals and for correlating functions of the second transition-metal atoms Y through Cd. A segmented contraction scheme is used for its compactness and efficiency. Contraction coefficients and exponents are determined by minimizing the deviation of the target function from the average of accurate atomic natural orbitals for the three lowest LS states arising from the 5s24d n-2, 5s1 4d n-1, and 5s0d n configurations. The present basis sets give a well balanced description for the three configurations at the Hartree—Fock level, and yield more than 97% of the atomic correlation energies predicted by accurate natural orbitals of the same size.

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.

Relativistic correlating basis sets for lanthanide atoms from Ce to Lu

Contracted Gaussian‐type function (CGTF) sets for the description of the 4f subshell correlation and of the 6s and 5d subshell correlation are developed for lanthanide atoms from Ce to Yb. Also prepared are basis sets for the 5d orbitals, which are vacant in the ground states of most lanthanide atoms but are essential in molecular environments. In addition, correlating CGTF sets for the 4f subshell correlation are supplemented for the Lu atom. 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 that include relativistic effects through the third‐order Douglas–Kroll approximation. All‐electron and model core potential calculations with the present correlating sets are performed on the ground state of the diatomic CeO molecule. The calculated spectroscopic constants are in good agreement with experimental values.

Relativistic correlating basis sets for the main group elements from Cs to Ra

Contracted Gaussian-type function sets are developed for correlating functions of the ten main group elements from Cs to Ra. A segmented contraction scheme is used for its compactness and efficiency. Contraction coefficients and exponents are determined by minimizing the deviation from accurate natural orbitals or K-orbitals, incorporating the relativistic effect by the third-order Douglas–Kroll approximation. The present basis sets yield more than 98% of atomic correlation energies predicted by accurate natural orbitals of the same size. The use of the present set with the model core potential methods gives more than 99% of the correlation energies obtained by the atomic natural orbitals optimized for the model core potential itself. The present correlating sets applied to relativistic model core potential methods including spin–orbit effects predict the spectroscopic constants of the BiH molecule in excellent agreement with experimental results.

Ab initio study of the lower few states of FeH: Application of the multireference coupled pair approximation

Multireference coupled pair approximation(4) [MRCPA(4)] was applied to describe the ground state and the lower excited states of FeH. This study demonstrates that the a 6Δ state is 0.27 eV above the ground state, X 4Δ, which is in good agreement with the observation (0.25 eV). The ground state is much more highly correlated than the a 6Δ state and the use of the size-consistent method is important to predict the relative stability accurately. In addition to the above results, spectroscopic data of the second 4Δ, the lowest 4Π, the lowest 4Φ, the lowest two 6Π, and the lowest 6Σ+ states are reported. The calculated excitation energies of the lowest 6Σ+ state and the second 4Δ state are in good agreement with results of experiment. The total energies of the lowest 4Δ, 4Π, 6Δ, 6Π, and 6Σ+ states are in the order of 4Δ<4Π<6Δ<6Π<6Σ+, which supports what was anticipated previously.

Relativistic correlating basis sets for actinide atoms from 90Th to 103Lr

For 14 actinide atoms from 90Th to 103Lr, contracted Gaussian‐type function sets are developed for the description of correlations of the 5f, 6d, and 7s electrons. Basis sets for the 6d orbitals are also prepared, since the orbitals are important in molecular environments despite their vacancy in the ground state of some actinides. A segmented contraction scheme is employed for the compactness and efficiency. Contraction coefficients and exponents are so determined as to minimize the deviation from accurate natural orbitals of the lowest term arising from the 5fn−16d17s2 configuration. The spin‐free relativistic effects are considered through the third‐order Douglas‐Kroll approximation. To test the present correlating sets, all‐electron calculations are performed on the ground state of 90ThO molecule. The calculated spectroscopic constants are in excellent agreement with experimental values.

On the electron-electron counterbalance hole

When a many-electron system has spatial inversion symmetry, the electron-electron counterbalance hole implies that two electrons with parallel spins cannot be at opposite positions with respect to the inversion center, and its presence was pointed out in the literature [T. Koga, J. Chem. Phys. 108, 2515 (1998)] for any pairs of Hartree-Fock orbitals with the same inversion parity. We report here a generalized result that in all two-electron systems with spatial inversion symmetry, the electron-electron counterbalance hole always exists for any approximate and exact wave functions with even inversion parity. The same is also true in momentum space. An extension of the hole to systems with three or more electrons is discussed.

Tables of accurate STF HF wavefunctions from B to Ca

Accurate Slater type function (STF) Hartree-Fock (HF) wavefunctions are calculated and tabled from B to Ca. The STFs have a form of rne-γr and the powers (n) of r are carefully determined. The total atomic energies agree with those of numerical HF (NHF) within the error of 4×10−6 a.u. and 1×10−5 a.u. for B to F and for Ne to Ca, respectively. The STF HF basis sets given will be useful to benchmark calculations for the molecular, solid, and atomic electronic states. Applications of the STF HF basis to molecular calculations are given and briefly discussed. Sample calculations are performed on the N2 and P2 molecules.

Structure and bonding of the (C6H6)+ 2 radical

To elucidate the relative stability of various structures of the benzene dimer cation radical, (C6H6)+ 2 in its ground and low-lying excited states, ab initio complete active space self-consistent field (CASSCF), multi-reference singly and doubly excited configuration interaction (MRSDCI), and multi-reference coupled pair approximation (MRCPA) calculations were performed. Full optimization was performed at the CASSCF level for various structures of the dimer cation, followed by MRSDCI and MRCPA calculations. It was found that the global minimum of the cation is at a slipped C2h sandwich structure but there are some other sandwich structures with almost the same stability, being within about kcal mol−1. T-shape structures are less stable than the sandwich structures, by more than 5 kcal mol−1 by MRCPA calculations. Low lying electronic excited states in various structures are also discussed.