Papers by Umpei Nagashima
Journal of Molecular Spectroscopy, May 27, 2015
Highly accurate 3D PESs have been calculated ab initio at the MR-SDCI+Q_DK3 level.From 3D PES, sp... more Highly accurate 3D PESs have been calculated ab initio at the MR-SDCI+Q_DK3 level.From 3D PES, spectroscopic parameters are calculated by perturbation and DVR methods.Calcd. spectroscopic parameters reproduced experimental values quite accurately.Ro-vibrationally averaged geometrical parameters are calculated as expectation value.Any tri-atomic, acyclic molecule is to be observed as being bent on ro-vib. average.The present work complements our previous study of the geometry and electronic structure in the ground and low-lying electronic states of FeCO. Here, we report three-dimensional potential energy surfaces (PESs) for the 3Σ-3Σ- electronic ground state and its high-spin counterpart, the excited state ã5Σ-, calculated ab initio at the MR-SDCI+Q _DK3/[5ZP ANO-RCC (Fe, C, O)] level of theory. These PESs are employed in 2nd-order-perturbation-theory and DVR3D calculations of the rotation–vibration energies and ro-vibrationally averaged structures. The equilibrium structures determined from the 3D PESs have rere(Fe–C) = 1.7247 Å, rere(C–O) = 1.1587 Å, and ∠e∠e(Fe–C–O) = 180° for the X̃3Σ- state, and rere(Fe–C) = 1.8429 Å, rere(C–O) = 1.1522 Å, and ∠e∠e(Fe–C–O) = 180° for the ã5Σ- state. The ro-vibrationally averaged structures, determined as expectation values over DVR3D wavefunctions, have 〈r〈r(Fe–C)〉0〉0 = 1.7303 Å, 〈r〈r(C–O)〉0〉0 = 1.1631 Å, and 〈∠〈∠(Fe–C–O)〉0〉0 = 172.6° for the X̃3Σ- state, and 〈r〈r(Fe–C)〉0〉0 = 1.8471 Å, 〈r〈r(C–O)〉0〉0 = 1.1568 Å, and 〈∠〈∠(Fe–C–O)〉0〉0 = 171.4° for the ã5Σ- state. The coordinate-covalent Fe–C bond in the X̃3Σ- state, which elongates significantly as the molecule bends, is shown to exhibit normal large amplitude bending motion with strong coupling (manifested by the large value of the relevant third order force constant) between bending and Fe–C stretching modes. The ionic Fe–C bond in the ã5Σ- state shows anormal bending behavior due to a severe Fermi resonance which also gives rise to a large coupling between the bending and the Fe–C stretching motions, even though the corresponding third order force constant is small. The Yamada–Winnewisser quasi-linearity parameter γ0γ0 is calculated to be −1.00 and −0.90, values characteristic for a linear molecule, for the X̃3Σ- and ã5Σ- states, respectively. The ro-vibrationally averaged structures of the X̃3Σ- state are discussed in detail and it is concluded that any triatomic, linear molecule will be observed as being bent on ro-vibrational average.
The Journal of Physical Chemistry, 1995
ABSTRACT
Proceedings of the 4th International Conference, Jun 1, 1990
New I/O technique for external auxiliary storage: magnetic disk unit, has been developed to impro... more New I/O technique for external auxiliary storage: magnetic disk unit, has been developed to improve the I/O performance on HITAC VOS3/ES1 with usual hardware architecture. Since the I/O technique is based on the idea that the sequence of I/O processes should be divided to some groups and be executed in parallel, and is quite similar to a pipeline on vector computer, we call it Parallel I/O (PIO).The PIO function has been realized and opened to end-users without any change to previous protocols.Comparison of actual performance of PIO with 16 degrees of parallelization (16 PIO), the speed of the PIO is about 26 times faster than the standard (sequential) I/O technique by using chained schedule function. In the case of 8 PIO, PIO is 13 times faster than the standard I/O technique. The efficiency of PIO correlates well with the degree of parallelization. Elapsed time is inversely proportional to the degree of parallelization. The change of acceleration ratio of PIO to the standard I/O is normally proportional to the degree of parallelization.The PIO is quite efficient for large scale supercomputing because I/O between external auxiliary storage and CPU is indispensable in large scale computations. Since the performance of I/O has not been improved, while the performance of supercomputer has made remarkable progress in CPU speed, I/O speed may become bottleneck for computations with supercomputers.
Biochimica Et Biophysica Acta Bioenergetics, 1992
Journal of Computer Chemistry Japan, 2005
Journal of Computer Chemistry, Japan, 2002
The Journal of Chemical Physics, 2009
The Journal of Physical Chemistry, 1992
ABSTRACT
Journal of Physical Chemistry, 1992
ABSTRACT
Chem Phys, 1985
Translational energy (Et ) spectra of Cl and HCl fragments from vinylchloride, trans-dichloroethy... more Translational energy (Et ) spectra of Cl and HCl fragments from vinylchloride, trans-dichloroethylene, cis-dichloroethylene, and 1,1'-dichloroethylene have been measured for the π*←π excitation at 193 nm. Et distribution and angular dependence of the Cl fragment indicate that the two-center dissociation occurs in a time faster than a rotation period and the recoiling organic radical (the counter fragment) is highly vibrationally excited. In dichloroethylenes, the presence of a second channel producing Cl atoms has been confirmed and attributed to the dissociation from the lower (n,σ*) state through a (π,σ*) state. The Et distribution of HCl fragments is nonstatistical and found to converge to null population at an energy less than half of the total available energy. This convergence point coincides with the value of the local available energy for the elimination reaction (activation energy —ΔH0reaction ). The yield of HCl molecules relative to Cl atoms is estimated to be ˜1.1 for vinylchloride. High efficiency of the HCl elimination is attributed to a rapid internal conversion from the (π,π*) state to the lowest (π,σ*) state from which the pathway to the transition state for HCl elimination is opened in ground electronic manifolds.
Chem Phys, 2002
The difference between the Ewald method for systems with three-dimensional periodicity and for th... more The difference between the Ewald method for systems with three-dimensional periodicity and for three-dimensional systems with two-dimensional periodicity [J. Chem. Phys. 115, 4457 (2001)] is described.
J Mol Spectrosc, 2008
Three-dimensional potential energy surfaces for the 2Delta electronic ground state of NiCN have b... more Three-dimensional potential energy surfaces for the 2Delta electronic ground state of NiCN have been calculated at the MR-SDCI+ Q+ Erel/[Roos ANO (Ni), aug-cc-pVQZ (C, N)] level of theory together with electric dipole moments and transition moments. From the ab initio data, standard molecular constants have been determined by the second-order perturbation method, rovibronic term values, rotational constants, and dipole moment expectation values have been determined by the variational RENNER program, and averaged structures have been computed with the variational MORBID method. The perturbation method failed because of a severe Fermi resonance between 2nu2 and nu3. The ab initio calculations yield a linear equilibrium structure with r(Ni-C)=1.8141 Å and r(C-N)=1.1665 Å. The zero-point averaged structure, determined as expectation values in terms of MORBID wavefunctions, is bent with <rho¯>0≡180°-<∠(Ni-C-N)>0=9(5)°,<r(Ni-C)>0=1.8159 Å, and <r(C-N)>0=1.1705 Å. The bending potential is shallow and gives rise to large-amplitude bending motion. Kingston et al. [C.T. Kingston, A.J. Merer, T.D. Varberg, J. Mol. Spectrosc. 215 (2002) 106-127] have obtained r(C-N)=1.1591(29) Å in LIF experiments, and Sheridan and Ziurys [P.M. Sheridan, L.M. Ziurys, J. Chem. Phys. 118 (2003) 6370-6379] obtained the value 1.1590(2) Å from microwave spectra. These experimentally derived r(C-N)-values are 'too short' when compared with <r(C-N)>0 but not so seriously short as in the cases of FeNC and CoCN.
Journal of Computer Chemistry Japan, 2005
The Journal of Chemical Physics, Apr 14, 2007
Journal of Computer Chemistry Japan, 2012
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Papers by Umpei Nagashima