[gmx-users] PMF

[Alex]

Dear gromacs user,

I am trying to simulate the PMF a small peptide adsorbed to a solid surface
but no success unfurtunatly.
For some force constant the peptide would not desorbed from the surface and
for higher force constants what you can see in enclosed file will happen.
Some question is:
If it is possible to somehow change the force constant for a coordinate
while pulling step? for example the first 1 ns by by k1 = 5000 and then
reduced to k1 = 1000 for the rest of pulling.

Also, the force constant in the pulling step and umbrella sampling do not
need to be the same necessarily?

How I can improve or increase the number of sampled frame?

 I have enclosed some results as well as mdp file and force in pulling step
in each step below, I would be so appreciated if you could guide me to
improve the results?

PMF result:
https://drive.google.com/open?id=0B_CbyhnbKqQDMC1Ua3BWLUZ3XzA

Force in pulling SMD
https://drive.google.com/open?id=0B_CbyhnbKqQDVWxkd2VLUmozUjg

position in pulling SMD
https://drive.google.com/open?id=0B_CbyhnbKqQDa0VKX0E0Zlp1ODA

Windows-com
https://drive.google.com/open?id=0B_CbyhnbKqQDR0poVlM2RTVSNG8

md-production.mdp
https://drive.google.com/open?id=0B_CbyhnbKqQDdGFRbWQzb29Nbmc

md-pulling.mdp
https://drive.google.com/open?id=0B_CbyhnbKqQDc2NPdlVmSmwydFk

nvt-umbrella.mdp
https://drive.google.com/open?id=0B_CbyhnbKqQDSk9LS2d2Q1pTN2s

npt-umbrella.mdp
https://drive.google.com/open?id=0B_CbyhnbKqQDVnB4STFxeENfREU

md-umbrella.mdp
https://drive.google.com/open?id=0B_CbyhnbKqQDQmFTZWRkR1BkcUE

Thank you very much in advance.

Regards,
Alex