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Journal Articles

Nuclear quantum effects of light and heavy water studied by all-electron first principles path integral simulations

Machida, Masahiko; Kato, Koichiro*; Shiga, Motoyuki

Journal of Chemical Physics, 148(10), p.102324_1 - 102324_11, 2018/03

AA2017-0553.pdf:4.95MB

Times Cited Count：19 Percentile：71.35(Chemistry, Physical)

The isotopologs of liquid water, H $_{2}$ O, D $_{2}$ O, and T $_{2}$ O, are studied systematically by first principles PIMD simulations, in which the whole entity of the electrons and nuclei are treated quantum mechanically. The simulation results are in reasonable agreement with available experimental data on isotope effects, in particular, on the peak shift in the radial distributions of H $_{2}$ O and D $_{2}$ O and the shift in the evaporation energies. It is found that, due to differences in nuclear quantum effects, the H atoms in the OH bonds more easily access the dissociative region up to the hydrogen bond center than the D (T) atoms in the OD (OT) bonds. The accuracy and limitation in the use of the current density-functional-theory-based first principles PIMD simulations are also discussed. It is argued that the inclusion of the dispersion correction or relevant improvements in the density functionals are required for the quantitative estimation of isotope effects.

Journal Articles

Calculation of heat capacities of light and heavy water by path-integral molecular dynamics

Shiga, Motoyuki; Shinoda, Wataru*

Journal of Chemical Physics, 123(13), p.134502_1 - 134502_8, 2005/10

https://doi.org/10.1063/1.2035078

Times Cited Count：46 Percentile：81.65(Chemistry, Physical)

In general, it has been a difficult issue to evaluate heat capacities of liquids and solids based on interatomic forces. This is because heat capacity involves a strong quantum effect especially at low temperatures. For example, it is known that conventional classical molecular dynamics method overestimates the heat capacity of water. In this report, we show that heat capacity can be calculated by path integral molecular dynamics method considering the quantum effect. The calculated heat capacities for the three states of water and its isotope effect have been found in good agreement with experiment at wide temperature range.

Journal Articles

Heat capacity of water; Path integral molecular dynamics approach

Shiga, Motoyuki

Ansanburu, 7(2), p.21 - 25, 2005/04

https://doi.org/10.11436/mssj1998.7.30_22

In general, quantitative estimation of heat capacity has been a difficult but an important issue in molecular simulation. This is because heat capacity involves quantum mechanics of atomic motions, particularly at the low temperature range. One of the useful approaches to such quantum systems is path integral simulation method. However, heat capacity, which is the dispersion of energy, is so computationally demanding that it was not feasible until the recent development of parallel computers and efficient algorithms. In this paper, we introduce a path integral molecular dynamics approach for the estimation of heat capacities, and apply this technique to three states of water.

Journal Articles