Hello to all I have tried to reproduce the hydration free energy (TI) of the ethanol from Hess and van der Vegt (JPCB, 110, 17616). The value I have obtained is around 20kJ/mol while the reference value is -20.1kJ/mol (if not the sign ...). If someone can help me find the mistake I would be very grateful. Below are the simulation details.
I followed the protocol of the paper, Berk: I used 47 lambda values (because of hydrogen bonds between solute-solvent) (dense near lambda=0 and between 0.46 and 0.72). I am turning off the LJ and Coulomb terms separately. Softcore (alpha = 0.5, power = 1), OPLS-AA Timestep = 2fs, sd = integrator, PME constrained = none trajectories = 40ps (NVT) (I know that is small, but I looking for qualitative results) after 20ps of equilibration (NPT). I have found a value of -4.8kJ/mol for the DeltaG(vacuum) (relative to mutate the ethanol to dummy in vacuum). My dv/dl curve (for DeltaG(water) is below. Should I expect this form? I think there are many "high" positive values. The numerical integration is 15.9kJ. So, DG(hyd) = DG(wat) - DG(vac) = 15.9 - (-4.8) = 20.7kJ I believe that this protocol is OK (but I want to confirm that). @ title "dG/d\8l\4" @ xaxis label "Time (ps)" @ yaxis label "dG/d\8l\4 (kJ mol\S-1\N [\8l\4]\S-1\N)" @TYPE xy 0.000 4.431073e+02 0.005 3.660083e+02 0.010 2.987275e+02 0.015 2.023206e+02 0.000 4.431073e+02 0.005 3.660083e+02 0.010 2.987275e+02 0.015 2.023206e+02 0.020 1.905198e+02 0.030 1.086573e+02 0.040 4.217960e+01 0.050 4.101856e+01 0.060 2.314358e+01 0.070 2.223774e+01 0.080 2.669019e+01 0.090 1.696131e+01 0.100 6.089735e+00 0.110 9.569030e+00 0.120 1.505562e+01 0.130 2.785974e+00 0.140 2.440906e+00 0.150 3.050463e+00 0.160 8.578429e-01 0.200 3.577259e+00 0.240 -3.532969e+00 0.280 5.842623e+00 0.320 7.912565e+00 0.360 9.322502e+00 0.400 -2.930754e+00 0.440 2.797944e+00 0.460 5.113900e+00 0.480 -3.919665e+00 0.500 -9.000282e+00 0.520 -7.636168e+00 0.540 -7.574299e+00 0.560 -2.144124e+01 0.580 -6.618514e+00 0.600 -2.755925e+01 0.620 -1.491331e+01 0.640 -2.541398e+01 0.660 -5.213154e+01 0.680 -2.364612e+01 0.700 -2.535817e+01 0.720 -7.767502e+00 0.760 -1.096362e+01 0.800 1.136031e+01 0.840 2.883933e+01 0.880 4.465743e+01 0.920 5.461566e+01 0.960 6.882000e+01 1.000 7.673736e+01 -- _______________________________________ Eudes Eterno Fileti Centro de Ciência Naturais e Humanas Universidade Federal do ABC Rua Catequese, 242 - 3º Andar 09090-400 Santo André - SP Brasil Tel: +55 11 4437-1600 ramal 408 skype: eefileti http://cromo.ufabc.edu.br/~fileti/
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