Dear all, I am studying the CH4-CO2-H2O mixture at low T(270K) and high P (20 bar).
Forcefields used: CH4 : Single point LJ site; CO2 : EPM2 (Rigid with two virtual sites); H2O: TIP4P. I computed the free energy of solvation for a CH4 molecule in H2O in the presence of CO2 at different concentrations. The BAR method was used for the calculation. I decoupled the CH4 molecule in 20 steps with lambda varying by 0.05 each step. Experiments have revealed that CO2 and CH4 are cosolvents for each other in water and CH4 solubility will increase in presence of CO2. However, I am getting more positive value for the free energy of solvation of CH4 when the CO2 concentration is increased. Based on the experimental data one would expect that the free energy becomes less positive (more negative) since CO2 was observed to enhance CH4 solubility. The forcefield combination used here was used earlier for studying CH4-CO2-H2O system, though in a different context where the authors simulated hydrate formation. So I guess the morels used are fine. I wonder whether the problems lies in my MDP file . The free energy calculation parameters used are given below. ; Free energy control stuff free_energy = yes init_lambda = 0.0 delta_lambda = 0 foreign_lambda = 0.05 sc-alpha = 0.5 sc-power = 1.0 sc-sigma = 0.373 ; equal to sigma of the single point CH4 model. couple-moltype = CH4 couple-lambda0 = vdw couple-lambda1 = none couple-intramol = no nstdhdl = 10 Any comment will be of great help. Regards, Sujith. -- Gromacs Users mailing list * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting! * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists * For (un)subscribe requests visit https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or send a mail to gmx-users-requ...@gromacs.org.