Biomedical subjects

Toshikatsu Koga

Publications and source records attributed to Toshikatsu Koga.

8 recordsLinked to original sources

PubMed2006

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.

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PubMed2005

Bounds to electron-pair relative and center-of-mass radii in many-electron atoms.

When the electron-electron interaction is explicitly considered in many-electron atoms, the average electron radius (r) splits into the inner (r<) and outer (r>) radii. It is shown that the sum and difference of these radii constitute upper and lower bounds, respectively, to the electron-pair relative distance r(12)=(/r1-r2/). An analogous result is also derived for the electron-pair center-of-mass radius (R)=(/r1+r2//2). For the 102 atoms He through Lr in their ground states, the tightness of these bounds is numerically examined at the Hartree-Fock limit level. Good linear correlations are observed between (r12) and (r>), and between (R) and (r>)/2.

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PubMed2004

Radial subshell splittings and double-zeta functions in many-electron atoms.

When the electron-electron interaction is explicitly considered in many-electron atoms, the average subshell radius nl splits into two different radii, inner radius nl and outer radius >nl, where n and l are the principal and azimuthal quantum numbers. For the 102 atoms He through Lr in their ground states, the radii nl and nl are systematically examined at the Hartree-Fock limit level. For a subshell nl, two exponents zeta nl(est) estimated from these radii have good linear correlations with variationally determined exponents zeta nl(var) of double-zeta Slater-type functions.

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PubMed2004

Average electron radii in many-electron atoms.

In many-electron atoms, the average electron radius r represents the mean distance of a single electron from the nucleus when all the interelectronic interactions are averaged. If the electron-electron interaction is explicitly considered, the average radius r splits into two different radii, inner radius r(<) and outer radius r(>). For the 102 atoms He through Lr in their ground states, the radii r(<) and r(>) are systematically examined at the Hartree-Fock limit level. The effect of electron correlations on r(<) and r(>) is also discussed for the He atom and its isoelectronic ions.

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PubMed2004

Bounds to average interelectronic angles in Hartree-Fock theory of atoms.

The average interelectronic is the expectation value of the angle thetaij (0 < or = thetaij < or = pi) subtended by the position vectors ri and rj of a pair of electrons i and j. In the Hartree-Fock theory of atoms, we point out that the angle and its subshell-pair components nl,n'l' are bounded from above and below, where n and l are the principal and azimuthal quantum numbers. The upper bounds for nl,n'l' with 0 < or = l, l' < or = 3 are 9pi/16 (=101.25 degrees), 135pi/256 (approximately 94.922 degrees), 265pi/512 (approximately 93.164 degrees), and 129pi/256 (approximately 90.703 degrees) for sp, pd, df, and sf pairs, respectively, while they are pi/2 (=90 degrees ) for the other ll' pairs, independent of n and n'. A weighted sum of these subshell-pair bounds gives an upper bound to . The lower bounds are pi/2 in all the cases.

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PubMed2004

Interelectronic angle densities of equivalent electrons in Hartree-Fock theory of atoms.

The interelectronic angle density A(theta12) is the probability density function that the angle thetaij (0 < or = thetaij < or = pi) subtended by the vectors ri and rj of any two electrons i and j becomes theta12. For equivalent electrons in atoms, it is shown that the density A(theta12) in the Hartree-Fock theory is given by a simple polynomial of cos theta12. Detailed expressions are reported for all LS terms arising from s2, pN (N = 2-6), dN (N = 2-10), and f(N) (N = 2,12) electron configurations. With no modifications, the present results apply as well to the interelectronic angle density A(theta12) in momentum space, where theta12 is the angle between two electron momenta.

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PubMed2004

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.

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PubMed2004

Quality of contracted Gaussian-type function basis sets.

The valence quality of contracted (C) Gaussian-type function (GTF) basis sets in molecular calculations is discussed for the first- through fourth-row atoms. The split-valence basis sets derived from minimal-type CGTF sets are compared with those derived from primitive (P) GTF sets. Using F, Cl, Br, and I atoms and their homonuclear diatomics as test species, we find that the split-valence CGTF sets have almost the same quality as PGTF sets with larger s and p expansion terms: for example, the (53/5), (533/53), (5333/533/5), and (53 333/5333/53) CGTF sets correspond approximately to the [9/5], [15/9], [19/15/5], and [22/18/7] PGTF sets for the first- to fourth-row atoms, respectively, where the slash separates the s, p, and d symmetries. For the main group atoms of the four rows, we recommend using the above-mentioned CGTFs or larger.

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