Dear gmx users,<br><br>Since I am new to surface tension topic I need to ask very trivial questions. Please help me out with these simple questions. <br><br>As
a starting point I am going to calculate surface tension of a pure
alkane in a cubic box and compare with experimental values.<br>
<br>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)<br><br>Can
anyone tell me what the difference between these two is?<br>
<br>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?<br>
<br>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)<br>
<br>Pcoupl = Parrinello-Rahman <br>Pcoupltype = isotropic <br>tau_p = 1 1 <br>compressibility = 4.5e-5 <br>ref_p = 40 <br>
<br><br>time period for which average is calculated Average RMSD Fluct. Drift Tot-Drift<br>-------------------------------------------------------------------------------<br>1-2000 ps run: #Surf*SurfTen 6.43844 3588.74 3588.35 0.091406 182.721<br>
500-2000 ps #Surf*SurfTen 12.8518 3605.72 3605.26 0.132126 198.189<br>1000-2000ps #Surf*SurfTen 18.8821 3610.97 3610.8 0.11819 118.191<br>1500-2000ps #Surf*SurfTen 23.0072 3585.51 3584.93 -0.444037 -222.019<br>
<br><br>
<br>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)? <br><br>5- Does box six affect the results? (mine is 3.3 nm ).<br><br><br>Thank you,<br>
<br>
<br><br><br><br><br><br>