R elativistic
many-body theory for atoms and molecules :
Heavy atom species are many-electron systems with
complicated state structures which push conventional
computational techniques to their limits. Relativistic
effects in these systems are so important that
conventional techniques are unsatisfactory; they
must be approached with a model which incorporates
relativity with quantum mechanics. In heavy-atom
systems, relativistic and electron correlation
effects are strongly intertwined. Therefore, approaches
that simultaneously account for both effects are
desirable. Correlation energy is that portion of
the total energy attributable to electron-electron
interaction which is not described in orbital models.
In heavy-atom systems the severity of these demands
increases. Fully relativistic many-body methods
which simultaneously account for both effects for
accurate determination of atomic and molecular
electronic structures are currently being developed
and tested using basis sets of either "local" or "global" functions.
During the last 15 years, we have been trying to
find suitable fully relativistic SCF and many-body
theories (e.g., relativistic many-body perturbation
theory and relativistic coupled cluster theory)
for atoms and molecules as a means of turning physical
pictures of electronic systems in which relativistic
effects are not negligible into ab initio computational
tools, and of extracting from the Dirac's relativistic
electron theory more nearly correct physical pictures.
Ab initio Monte
Carlo and molecular dynamics studies of structure
and dynamics of polyatomic systems : In
recent years, metal, semiconductor and molecular
clusters have received attention because they differ
physically and chemically from bulk state and their
study can have practical uses in catalysis and
material science. The major difficulty in computer
simulations of metal, semiconductor and molecular
clusters is the description of the many-body interactions.
The pair-wise approximation commonly used to describe
the system does not work well for covalent and
metallic systems where many-body interactions play
a crucial role. We have developed ab
initio molecular dynamics and Monte Carlo simulated annealing algorithms
that describe the many-body interactions in metal, semiconductor and molecular
clusters in terms of ab initio correlated method at the level of CAS
SCF and second-order Møller-Plesset perturbation theory.
Selected Publications
- H-Atom Abstraction From CH 3NHNH 2 by NO
2: CCSD(T)/6-311++G(3df,2p//MPWB1K/ 6-31+G(d,p)
and CCSD(T)/6-311+G(2df,p)//CCSD/6-31+G(d,p)
Calculations, M. J. McQuaid and Y. Ishikawa,
J. Phys. Chem. A110 (2006) 6129.
- Relativistic
multireference many-body perturbation theory
calculations on F-, Ne-, Na-, Mg-, Al-, Si-,
and P-like Xe ions, M. J. Vilkas, Y. Ishikawa
and E. Traebert, J. Phy. B39 (2006) 2195.
- Density-functional
theoretical study on hydrated DNA duplex: Effect
of solvating water molecules on HOMO distribution
in DNA, T. Tsukamoto, Y. Ishikawa, M. J. Vilkas,
T. Natsume, K. Dedachi, and N. Kurita, Chem.
Phys. Letters, 429 (2006) 563.
- Atomic transition
energies and the variation of the fine-structure
constant α, A. Borschevsky, E. Eliav, Y.
Ishikawa, and U. Kaldor, Phys. Rev. A 74 (2006)
062504.
- Relativistic multireference many-body
perturbation theory calculations on Au 64+
- Au 69+ ions, M. J. Vilkas, Y. Ishikawa, and
E. Traebert, Eur. Phys. J. D 41 (2007) 77.
- Hybridization
energies of double strands composed of DNA,
RNA, PNA and LNA, T. Natsume, Y. Ishikawa, K.
Dedachi, T. Tsukamoto, and N. Kurita, Chem. Phys.
Letters, 434 (2007) 133
- Charge Transfer Through
Single- and Double-strand DNA: Simulations
Based on Molecular Dynamics and Molecular Orbital
Methods, K. Dedachi, T. Natsume, T. Nakatsu,
S. Tanaka, Y. Ishikawa, and N. Kurita, Chem.
Phys. Letters, 436 (2007) 244.
- Transition energies
of atomic Lawrencium, A. Borschevsky, E. Eliav,
M. J. Vilkas, Y. Ishikawa, U. Kaldor, Eur.
Phys. J., 45 (2007) 115.
- Relativistic R-matrix
close-coupling method based on the effective
Hamiltonian in many-body perturbation theory,
M. J. Vilkas and Y. Ishikawa, Phys. Rev. A
75 (2007) 062508.
- Direct molecular dynamics and density-functional
theoretical study of electrochemical hydrogen
oxidation reaction and underpotential deposition
of H on Pt(111), Y. Ishikawa, J. J. Mateo, D.
A. Tryk, C. R. Cabrera, J. of Electroanal. Chem.
607 (2007) 37.
- Predicted spectrum of atomic nobelium,
A. Borschevsky, E. Eliav, M. J. Vilkas, Y.
Ishikawa, U. Kaldor, Phys. Rev. A 75 (2007) 042514.
- A combined MD/DFT study on the structures and
electronic properties of hydrating water molecules
in the minor groove of a decameric DNA duplex,
T. Tsukamoto, Y. Ishikawa, T. Natsume, K. Dedachi,
and N. Kurita, Chem. Phys. Letters, 441 (2007)
136.
- A Fock space coupled cluster study on
the electronic structure of the UO 2, UO
2 +, U 4+, and U 5+ species , Ivan Infante, Ephraim
Eliav, Marius J. Vilkas, Yasuyuki Ishikawa,
Uzi Kaldor, and Lucas Visscher, J. Chem.
Phys. 126 (2007) 184305.
- Effect of base mismatch on the hybridizations
of DNA-DNA and LNA-DNA double strands: DFT molecular
orbital calculations, T. Natsume, Y. Ishikawa,
K. Dedachi, T. Tsukamoto, and N. Kurita, Chem.
Phys. Letters, 446 (2007) 151.
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