In the present paper, a generalized hybrid Monte Carlo method to generate the multicanonical ense... more In the present paper, a generalized hybrid Monte Carlo method to generate the multicanonical ensemble has been developed, which is a generalization of the multicanonical hybrid Monte Carlo (HMC) method by Hansmann and co-workers [Chem. Phys. Lett. 259, 321 (1996)]. The generalized hybrid Monte Carlo (GHMC) method is an equations-of-motion guided Monte Carlo combined with partial momentum refreshment. We successfully applied our multicanonical GHMC to dense Lennard-Jones fluids and a coarse grained protein model. It is found that good computational efficiency can be gained in the case of the acceptance ratio around 60% for the models examined. While a large number of molecular dynamics (MD) steps in a single GHMC cycle is needed to yield good computational efficiency at a large mixing ratio of momenta with thermal noise vectors, corresponding to the original multicanonical HMC method, a small number of MD steps are enough to achieve good efficiency at a small mixing ratio. This property is useful to develop a composite algorithm combining the present GHMC method with other Monte Carlo moves.
Path integral instanton method is a promising way to calculate the tunneling splitting of energie... more Path integral instanton method is a promising way to calculate the tunneling splitting of energies for degenerated two state systems. In order to calculate the tunneling splitting, we need to take the zero temperature limit, or the limit of infinite imaginary time duration. In the method developed by Richardson and Althorpe [J. Chem. Phys. 134, 054109 (2011)], the limit is simply replaced by the sufficiently long imaginary time. In the present study, we have developed a new formula of the tunneling splitting based on the discretized path integrals to take the limit analytically. We have applied our new formula to model systems, and found that this approach can significantly reduce the computational cost and gain the numerical accuracy. We then developed the method combined with the electronic structure calculations to obtain the accurate interatomic potential on the fly. We present an application of our ab initio instanton method to the ammonia umbrella flip motion.
Microscopic structure of small helium-4 clusters doped with a carbonyl sulfide molecule, OCS(4 He... more Microscopic structure of small helium-4 clusters doped with a carbonyl sulfide molecule, OCS(4 He) N , at 0.37 K is studied by the path integral hybrid Monte Carlo method; the size of the cluster N ranges from N = 2 to N = 5. In all the cases examined in the present study, the helium atoms are localized around the carbon atom of the OCS molecule, forming a doughnut-type structure around the molecular axis. Bosonic exchange among the helium atoms is found to be promoted in the doughnut region, showing an anisotropic "superfluid" response of the clusters.
... DM Ceperley, Path integrals in the theory of condensed helium, Rev. ... MP Allen and DJ Til... more ... DM Ceperley, Path integrals in the theory of condensed helium, Rev. ... MP Allen and DJ Tildesley, Computer Simulation of Liquids (Oxford University Press, Oxford, 1987). SW Lovesey, Condensed Matter Physics: Dynamic Correlations (Benjamin-Cummings, Menlo Park, 1986). ...
In this paper, we present a path integral hybrid Monte Carlo ͑PIHMC͒ method for rotating molecule... more In this paper, we present a path integral hybrid Monte Carlo ͑PIHMC͒ method for rotating molecules in quantum fluids. This is an extension of our PIHMC for correlated Bose fluids ͓S. Miura and J. Tanaka, J. Chem. Phys. 120, 2160 ͑2004͔͒ to handle the molecular rotation quantum mechanically. A novel technique referred to be an effective potential of quantum rotation is introduced to incorporate the rotational degree of freedom in the path integral molecular dynamics or hybrid Monte Carlo algorithm. For a permutation move to satisfy Bose statistics, we devise a multilevel Metropolis method combined with a configurational-bias technique for efficiently sampling the permutation and the associated atomic coordinates. Then, we have applied the PIHMC to a helium-4 cluster doped with a carbonyl sulfide molecule. The effects of the quantum rotation on the solvation structure and energetics were examined. Translational and rotational fluctuations of the dopant in the superfluid cluster were also analyzed.
In this paper, solvation structure and thermodynamic properties of rare gas and alkali impurities... more In this paper, solvation structure and thermodynamic properties of rare gas and alkali impurities in liquid helium-4 have been studied theoretically. A generalized Ornstein–Zernike integral equation for pure quantum fluids [J. Chem. Phys. 114, 7497 (2001)] was extended to the quantum solutions at infinite dilution. Self-correlation function of the solute atom which appears in the integral equation was determined self-consistently with the solvent density fluctuation. Numerical calculations have been performed for the helium-4 solutions at 4 K, with Boltzmann statistics being assumed. It was found that all the rare gas species investigated in this study have negative partial molar volumes, owing to the well-defined solvation structure around the impurities. In contrast to this, the alkali atoms have large positive partial molar volumes, primarily coming from the excluded volume contribution. Further, while the rare gas atoms have negative excess chemical potentials, the alkali atoms have large positive val...
ABSTRACT Large-scale and long-time molecular dynamics calculations have been performed using a fl... more ABSTRACT Large-scale and long-time molecular dynamics calculations have been performed using a fluctuating charge model TIP4P-FQ in order to investigate structure and dynamics of supercritical water near the critical point. The calculated Ornstein–Zernike behavior of the structure factor S(k) in the small wave number region was in satisfactory agreement with experiment. The intermediate scattering function F(k,t) showed much slower decay in the supercritical water than that found in the ambient water. Further, the calculated dynamic structure factor S(k,ω) clearly showed the existence of acoustic mode for both systems. The calculated dispersion relation for the liquid water is in good agreement with the IXS data. In the supercritical water near the critical point, the acoustic excitation propagates with a speed of about 420 m/s.
The equation of state (EOS) and critical constants are reported for a fluctuating-charge model of... more The equation of state (EOS) and critical constants are reported for a fluctuating-charge model of water, based on PρT data from a series of molecular dynamics (MD) calculations. Since unphysical divergence of the partial charges sometimes occurred in the course of MD calculations, the model (TIP4P-FQ) was slightly modified to avoid this erroneous behavior. The EOS was determined by fitting the calculated PρT data to a model EOS. The calculated critical constants are in good agreement with the experimental values.
In the present Letter, novel molecular dynamics methods compatible with corresponding quantum Mon... more In the present Letter, novel molecular dynamics methods compatible with corresponding quantum Monte Carlo methods are developed. One is a variational molecular dynamics method that is a molecular dynamics analog of quantum variational Monte Carlo method. The other is a variational path integral molecular dynamics method, which is based on the path integral molecular dynamics method for finite temperature systems by Tuckerman et al., J. Chem. Phys. 99, 2796 (1993). These methods are applied to model systems including the liquid helium-4, demonstrated to work satisfactorily for the tested ground state calculations.
A series of molecular dynamics calculations of supercritical (SC) water along an isotherm at 600 ... more A series of molecular dynamics calculations of supercritical (SC) water along an isotherm at 600 K have been performed using a polarizable potential model. A relatively large system composed of 100...
Potential energy landscape and thermodynamic transitions of coarse-grained protein models reveale... more Potential energy landscape and thermodynamic transitions of coarse-grained protein models revealed by the multicanonical generalized hybrid Monte Carlo method
In the present paper, a generalized hybrid Monte Carlo method to generate the multicanonical ense... more In the present paper, a generalized hybrid Monte Carlo method to generate the multicanonical ensemble has been developed, which is a generalization of the multicanonical hybrid Monte Carlo (HMC) method by Hansmann and co-workers [Chem. Phys. Lett. 259, 321 (1996)]. The generalized hybrid Monte Carlo (GHMC) method is an equations-of-motion guided Monte Carlo combined with partial momentum refreshment. We successfully applied our multicanonical GHMC to dense Lennard-Jones fluids and a coarse grained protein model. It is found that good computational efficiency can be gained in the case of the acceptance ratio around 60% for the models examined. While a large number of molecular dynamics (MD) steps in a single GHMC cycle is needed to yield good computational efficiency at a large mixing ratio of momenta with thermal noise vectors, corresponding to the original multicanonical HMC method, a small number of MD steps are enough to achieve good efficiency at a small mixing ratio. This property is useful to develop a composite algorithm combining the present GHMC method with other Monte Carlo moves.
Path integral instanton method is a promising way to calculate the tunneling splitting of energie... more Path integral instanton method is a promising way to calculate the tunneling splitting of energies for degenerated two state systems. In order to calculate the tunneling splitting, we need to take the zero temperature limit, or the limit of infinite imaginary time duration. In the method developed by Richardson and Althorpe [J. Chem. Phys. 134, 054109 (2011)], the limit is simply replaced by the sufficiently long imaginary time. In the present study, we have developed a new formula of the tunneling splitting based on the discretized path integrals to take the limit analytically. We have applied our new formula to model systems, and found that this approach can significantly reduce the computational cost and gain the numerical accuracy. We then developed the method combined with the electronic structure calculations to obtain the accurate interatomic potential on the fly. We present an application of our ab initio instanton method to the ammonia umbrella flip motion.
Microscopic structure of small helium-4 clusters doped with a carbonyl sulfide molecule, OCS(4 He... more Microscopic structure of small helium-4 clusters doped with a carbonyl sulfide molecule, OCS(4 He) N , at 0.37 K is studied by the path integral hybrid Monte Carlo method; the size of the cluster N ranges from N = 2 to N = 5. In all the cases examined in the present study, the helium atoms are localized around the carbon atom of the OCS molecule, forming a doughnut-type structure around the molecular axis. Bosonic exchange among the helium atoms is found to be promoted in the doughnut region, showing an anisotropic "superfluid" response of the clusters.
... DM Ceperley, Path integrals in the theory of condensed helium, Rev. ... MP Allen and DJ Til... more ... DM Ceperley, Path integrals in the theory of condensed helium, Rev. ... MP Allen and DJ Tildesley, Computer Simulation of Liquids (Oxford University Press, Oxford, 1987). SW Lovesey, Condensed Matter Physics: Dynamic Correlations (Benjamin-Cummings, Menlo Park, 1986). ...
In this paper, we present a path integral hybrid Monte Carlo ͑PIHMC͒ method for rotating molecule... more In this paper, we present a path integral hybrid Monte Carlo ͑PIHMC͒ method for rotating molecules in quantum fluids. This is an extension of our PIHMC for correlated Bose fluids ͓S. Miura and J. Tanaka, J. Chem. Phys. 120, 2160 ͑2004͔͒ to handle the molecular rotation quantum mechanically. A novel technique referred to be an effective potential of quantum rotation is introduced to incorporate the rotational degree of freedom in the path integral molecular dynamics or hybrid Monte Carlo algorithm. For a permutation move to satisfy Bose statistics, we devise a multilevel Metropolis method combined with a configurational-bias technique for efficiently sampling the permutation and the associated atomic coordinates. Then, we have applied the PIHMC to a helium-4 cluster doped with a carbonyl sulfide molecule. The effects of the quantum rotation on the solvation structure and energetics were examined. Translational and rotational fluctuations of the dopant in the superfluid cluster were also analyzed.
In this paper, solvation structure and thermodynamic properties of rare gas and alkali impurities... more In this paper, solvation structure and thermodynamic properties of rare gas and alkali impurities in liquid helium-4 have been studied theoretically. A generalized Ornstein–Zernike integral equation for pure quantum fluids [J. Chem. Phys. 114, 7497 (2001)] was extended to the quantum solutions at infinite dilution. Self-correlation function of the solute atom which appears in the integral equation was determined self-consistently with the solvent density fluctuation. Numerical calculations have been performed for the helium-4 solutions at 4 K, with Boltzmann statistics being assumed. It was found that all the rare gas species investigated in this study have negative partial molar volumes, owing to the well-defined solvation structure around the impurities. In contrast to this, the alkali atoms have large positive partial molar volumes, primarily coming from the excluded volume contribution. Further, while the rare gas atoms have negative excess chemical potentials, the alkali atoms have large positive val...
ABSTRACT Large-scale and long-time molecular dynamics calculations have been performed using a fl... more ABSTRACT Large-scale and long-time molecular dynamics calculations have been performed using a fluctuating charge model TIP4P-FQ in order to investigate structure and dynamics of supercritical water near the critical point. The calculated Ornstein–Zernike behavior of the structure factor S(k) in the small wave number region was in satisfactory agreement with experiment. The intermediate scattering function F(k,t) showed much slower decay in the supercritical water than that found in the ambient water. Further, the calculated dynamic structure factor S(k,ω) clearly showed the existence of acoustic mode for both systems. The calculated dispersion relation for the liquid water is in good agreement with the IXS data. In the supercritical water near the critical point, the acoustic excitation propagates with a speed of about 420 m/s.
The equation of state (EOS) and critical constants are reported for a fluctuating-charge model of... more The equation of state (EOS) and critical constants are reported for a fluctuating-charge model of water, based on PρT data from a series of molecular dynamics (MD) calculations. Since unphysical divergence of the partial charges sometimes occurred in the course of MD calculations, the model (TIP4P-FQ) was slightly modified to avoid this erroneous behavior. The EOS was determined by fitting the calculated PρT data to a model EOS. The calculated critical constants are in good agreement with the experimental values.
In the present Letter, novel molecular dynamics methods compatible with corresponding quantum Mon... more In the present Letter, novel molecular dynamics methods compatible with corresponding quantum Monte Carlo methods are developed. One is a variational molecular dynamics method that is a molecular dynamics analog of quantum variational Monte Carlo method. The other is a variational path integral molecular dynamics method, which is based on the path integral molecular dynamics method for finite temperature systems by Tuckerman et al., J. Chem. Phys. 99, 2796 (1993). These methods are applied to model systems including the liquid helium-4, demonstrated to work satisfactorily for the tested ground state calculations.
A series of molecular dynamics calculations of supercritical (SC) water along an isotherm at 600 ... more A series of molecular dynamics calculations of supercritical (SC) water along an isotherm at 600 K have been performed using a polarizable potential model. A relatively large system composed of 100...
Potential energy landscape and thermodynamic transitions of coarse-grained protein models reveale... more Potential energy landscape and thermodynamic transitions of coarse-grained protein models revealed by the multicanonical generalized hybrid Monte Carlo method
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Papers by Shinichi MIURA