The nature of the calculation of the pressure in molecular simulations of continuous models from volume perturbations

Abstract

We consider some fundamental aspects of the calculation of the pressure from simulations by performing volume perturbations. The method, initially proposed for hard-core potentials by Eppenga and Frenkel ͓Mol. Phys. 52, 1303 ͑1984͔͒ and then extended to continuous potentials by Harismiadis et al. ͓J. Chem. Phys. 105, 8469 ͑1996͔͒, is based on the numerical estimate of the change in Helmholtz free energy associated with the perturbation which, in turn, can be expressed as an ensemble average of the corresponding Boltzmann factor. The approach can be easily generalized to the calculation of components of the pressure tensor and also to ensembles other than the canonical ensemble. The accuracy of the method is assessed by comparing simulation results obtained from the volume-perturbation route with those obtained from the usual virial expression for several prototype fluid models. Monte Carlo simulation data are reported for bulk fluids and for inhomogeneous systems containing a vapor-liquid interface.

Interfacial properties of selected binary mixtures containing n-alkanes

“…19, the equilibrated system (state 0) with interfacial area According to our results, we found that γ is constant in the range 10 -5 < ξ < 10 -3 . The value of ξ used in this work is 5 × 10 -4 , which is commensurate with previous other similar application of the TA method [68,[71][72][73][74][75] . All the TA calculations are performed by post-processing an uninterrupted MD run, as the perturbations have no effect on the dynamics of the system.…”

Note: Free energy calculations for atomic solids through the Einstein crystal/molecule methodology using GROMACS and LAMMPS

“…For the LJ/STS system A 0 , ∆ A 1 , and ∆ A 2 obtained from MC and from MD (GRO-MACS/LAMMPS) are in very good agreement, with a free energy difference lower than 0.03 N k B T (typical uncertainties in calculations of free energy of solids being of 0.05 N k B T ). The choice of a LJ spherically truncated and shifted (STS) avoids the subtle issues arising when comparing results obtained by MC and MD for a spherically truncated (ST) potential [5,16,17]. In the LJ/ST truncated at r c = 5σ, the free energy results obtained with MC and MD agree quite well with each other and with previous calculations for the same system size and thermodynamic state [2,18,19].…”

Surface tension of the most popular models of water by using the test-area simulation method

“…A similar free-energy perturbation approach has been considered for the calculation of the bulk pressure 46 or the components of the pressure tensor. [47][48][49] Gloor et al 42 have shown that the test-area method can be used for simple systems ͑LJ or square wells͒ with results in full agreement with those obtained from the conventional virial route. They have also shown that the methodology can be used for molecular fluids such as the Gay Berne model.…”