MOLECULAR DYNAMICS AT CONSTANT PRESSURE AND TEMPERATURE

Methods are discussed for generating by molecular dynamics isobaric-isoenthalpic, NPH, isochoric-isothermal, NVT, and isobaric-isothermal, NPT, ensembles. Andersen's constant-pressure method is reformulated so that the ensemble rather than the scaled system is directly calculated. Four constant-temperature schemes were considered. Two involve the addition of a stochastic collision term to the molecular trajectories. The Andersen method and a stochastic dynamics approach were examined. The latter employed a velocity damping term in addition to the random force. Two other methods employed uniform velocity scaling applied to all molecules. The NPT algorithm induces a transition to the dilute phase for a Lennard-Jones fluid in the spinodal region (p* = 0.5, T* = 1.28) of the phase diagram. The thermodynamic equivalence of the ensembles is demonstrated by long calculations of the chemical potential of Lennard-Jones states by the particle insertion method. The internal energy, pressure, constant volume and pressure specific heats, adiabatic compressibilities, pair radial distribution functions and self-diffusion coefficients are also evaluated. Only for second-order thermodynamic quantities is there evidence of an ensemble dependence.

[1]  H. Berendsen,et al.  On the fluctuation-dissipation theorem for interacting brownian particles , 1982 .

[2]  M. Parrinello,et al.  Polymorphic transitions in single crystals: A new molecular dynamics method , 1981 .

[3]  I. R. Mcdonald,et al.  An equation of state for simple liquids , 1972 .

[4]  J. D. Doll,et al.  Brownian dynamics as smart Monte Carlo simulation , 1978 .

[5]  J. Weeks,et al.  Constant pressure molecular dynamics simulations of the 2Dr−12 system: Comparison with isochores and isotherms , 1981 .

[6]  D. Lévesque,et al.  Transport properties and the time evolution of electrolyte solutions in the Brownian dynamics approximation , 1979 .

[7]  D. J. Tildesley,et al.  Equation of state for the Lennard-Jones fluid , 1979 .

[8]  H. C. Andersen Molecular dynamics simulations at constant pressure and/or temperature , 1980 .

[9]  L. V. Woodcock Isothermal molecular dynamics calculations for liquid salts , 1971 .

[10]  David Fincham,et al.  Molecular dynamics simulation using the cray-1 vector processing computer , 1981 .

[11]  J. Haile,et al.  Extensions of the molecular dynamics simulation method. II. Isothermal systems , 1983 .

[12]  J. Doll,et al.  Generalized Langevin equation approach for atom/solid–surface scattering: Numerical techniques for Gaussian generalized Langevin dynamics , 1976 .

[13]  Koichiro Nakanishi,et al.  Constant temperature molecular dynamics calculation on Lennard‐Jones fluid and its application to watera) , 1983 .

[14]  J. M. Haile,et al.  Molecular dynamics simulations extended to various ensembles. I. Equilibrium properties in the isoenthalpic–isobaric ensemble , 1980 .

[15]  D. J. Adams,et al.  Calculating the high-temperature vapour line by Monte Carlo , 1976 .

[16]  J. G. Powles,et al.  Non-destructive molecular-dynamics simulation of the chemical potential of a fluid , 1982 .

[17]  F. Vesely,et al.  Atomic pair dynamics in a Lennard-Jones fluid: Comparison of theory with computer simulation , 1981 .