Simple quantitative tests to validate sampling from thermodynamic ensembles Michael R. Shirts∗ Department of Chemical Engineering, University of Virginia, VA 22904 E-mail:
[email protected] Abstract It is often difficult to quantitatively determine if a new molecular simulation algorithm or software properly implements sampling of the desired thermodynamic ensemble. We present some simple statistical analysis procedures to allow sensitive determination of whether a de- sired thermodynamic ensemble is properly sampled. We demonstrate the utility of these tests for model systems and for molecular dynamics simulations in a range of situations, includ- ing constant volume and constant pressure simulations, and describe an implementation of the tests designed for end users. 1 Introduction Molecular simulations, including both molecular dynamics (MD) and Monte Carlo (MC) tech- arXiv:1208.0910v1 [cond-mat.stat-mech] 4 Aug 2012 niques, are powerful tools to study the properties of complex molecular systems. When used to specifically study thermodynamics of such systems, rather than dynamics, the primary goal of molecular simulation is to generate uncorrelated samples from the appropriate ensemble as effi- ciently as possible. This simulation data can then be used to compute thermodynamic properties ∗To whom correspondence should be addressed 1 of interest. Simulations of several different ensembles may be required to simulate some thermo- dynamic properties, such as free energy differences between states. An ever-expanding number of techniques have been proposed to perform more and more sophisticated sampling from com- plex molecular systems using both MD and MC, and new software tools are continually being introduced in order to implement these algorithms and to take advantage of advances in hardware architecture and programming languages.