Biomedical subjects

Kenichi Kinugawa

Publications and source records attributed to Kenichi Kinugawa.

5 recordsLinked to original sources

PubMed2005

Effective potential analytic continuation approach for real time quantum correlation functions involving nonlinear operators.

We apply the effective potential analytic continuation (EPAC) method to the calculation of real time quantum correlation functions involving operators nonlinear in the position operator q. For a harmonic system the EPAC method provides the exact correlation function at all temperature ranges, while the other quantum dynamics methods, the centroid molecular dynamics and the ring polymer molecular dynamics, become worse at lower temperature. For an asymmetric anharmonic system, the EPAC correlation function is in very good agreement with the exact one at t = 0. When the time increases from zero, the EPAC method gives good coincidence with the exact result at lower temperature. Finally, we propose a simplified version of the EPAC method to reduce the computational cost required for the calculation of the standard effective potential.

Journal Article↗

PubMed2004

Quantum effect on the internal proton transfer and structural fluctuation in the H+ 5 cluster.

The thermal equilibrium state of H+(5) is investigated by means of an ab initio path integral molecular dynamics (PIMD) method, in which degrees of freedom of both nuclei and electrons at finite temperature are quantized within the adiabatic approximation. The second-order Moller-Plesset force field has been employed for the present ab initio PIMD. At 5-200 K, H+(5) is shown to have the structure that the proton is surrounded by the two H(2) units without any exchange of an atom between the central proton and the H(2) unit. At 5 K, the quantum tunneling of the central proton occurs more easily when the distance between the two H(2) units is shortened. At the high temperature of 200 K, the central proton is more delocalized in space between the two H(2) units, with less correlation with the stretching of the distance between the two H(2) units. As for the rotation of the H(2) units around the C(2) axis of H+(5) , the dihedral angle distribution is homogeneous at all temperatures, suggesting that the two H(2) units freely rotate around the C(2) axis, while this quantum effect on the rotation of the H(2) units becomes more weakened with increasing temperature. The influence of the structural fluctuation of H+(5) on molecular orbital energies has been examined to conclude that the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap is largely reduced with the increase of temperature because of the spatial expansion of the whole cluster.

Journal Article↗

PubMed2004

Effective potential analytic continuation calculations of real time quantum correlation functions: asymmetric systems.

We apply the effective potential analytic continuation (EPAC) method to one-dimensional asymmetric potential systems to obtain the real time quantum correlation functions at various temperatures. Comparing the EPAC results with the exact results, we find that for an asymmetric anharmonic oscillator the EPAC results are in very good agreement with the exact ones at low temperature, while this agreement becomes worse as the temperature increases. We also show that the EPAC calculation for a certain type of asymmetric potentials can be reduced to that for the corresponding symmetric potentials.

Journal Article↗

PubMed2004

Centroid molecular dynamics approach to the transport properties of liquid para-hydrogen over the wide temperature range.

Fundamental transport properties of liquid para-hydrogen (p-H(2)), i.e., diffusion coefficients, thermal conductivity, shear viscosity, and bulk viscosity, have been evaluated by means of the path integral centroid molecular dynamics (CMD) calculations. These transport properties have been obtained over the wide temperature range, 14-32 K. Calculated values of the diffusion coefficients and the shear viscosity are in good agreement with the experimental values at all the investigated temperatures. Although a relatively large deviation is found for the thermal conductivity, the calculated values are less than three times the amount of the experimental values at any temperature. On the other hand, the classical molecular dynamics has led all the transport properties to much larger deviation. For the bulk viscosity of liquid p-H(2), which was never known from experiments, the present CMD has given a clear temperature dependence. In addition, from the comparison based on the principle of corresponding states, it has been shown that the marked deviation of the transport properties of liquid p-H(2) from the feature which is expected from the molecular parameters is due to the quantum effect.

Journal Article↗

PubMed2004

Ab initio centroid path integral molecular dynamics: application to vibrational dynamics of diatomic molecular systems.

An ab initio centroid molecular dynamics (CMD) method is developed by combining the CMD method with the ab initio molecular orbital method. The ab initio CMD method is applied to vibrational dynamics of diatomic molecules, H2 and HF. For the H2 molecule, the temperature dependence of the peak frequency of the vibrational spectral density is investigated. The results are compared with those obtained by the ab initio classical molecular dynamics method and exact quantum mechanical treatment. It is shown that the vibrational frequency obtained from the ab initio CMD approaches the exact first excitation frequency as the temperature lowers. For the HF molecule, the position autocorrelation function is also analyzed in detail. The present CMD method is shown to well reproduce the exact quantum result for the information on the vibrational properties of the system.

Journal Article↗