Dear gmx users, Since I am new to surface tension topic I need to ask very trivial questions. Please help me out with these simple questions.
As a starting point I am going to calculate surface tension of a pure alkane in a cubic box and compare with experimental values. 1- g_energy is giving #Surf*SurfTen by default. On the other hand surface tension can be obtained by gamma = (Pzz - (Pxx+Pyy)/2) / Lz. i.e Pres-XX-(bar), Pres-YY(bar), Pres--(bar) Can anyone tell me what the difference between these two is? 2- In pressure coupling settings there is surface_tension option which I guess is applicable where surface tension needs to be kept fixed. If one want to calculate surface tension I dont think this option make sense. Am I right? 3- I am using the following setting: I calculate the average for a 2ns run and different start times as shown below. Although T, P and other quantities are equilibrated after 200ps, surface tension is not giving a constant value. Is that because I am not using berenden P coupling? (As mentioned in the manual surface tension works with berendsen) Pcoupl = Parrinello-Rahman Pcoupltype = isotropic tau_p = 1 1 compressibility = 4.5e-5 ref_p = 40 time period for which average is calculated Average RMSD Fluct. Drift Tot-Drift ------------------------------------------------------------------------------- 1-2000 ps run: #Surf*SurfTen 6.43844 3588.74 3588.35 0.091406 182.721 500-2000 ps #Surf*SurfTen 12.8518 3605.72 3605.26 0.132126 198.189 1000-2000ps #Surf*SurfTen 18.8821 3610.97 3610.8 0.11819 118.191 1500-2000ps #Surf*SurfTen 23.0072 3585.51 3584.93 -0.444037 -222.019 4- Assuming I am getting surface tension for a cubic box, to compare this with reported values in literature I need to divide by 6 (no. of surfaces)? 5- Does box six affect the results? (mine is 3.3 nm ). Thank you,
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