Determining the PMF with Adaptive Biasing Forces

From: sunyzero (sunyzero_at_163.com)
Date: Mon Dec 07 2015 - 20:02:35 CST

Dear Namd users
   Hello, I need your help about determining the PMF with Adaptive Biasing Forces. According to tutorial about Methods for calculating Poteintials of Mean Force, I use it on HIV-1 protease inhibitors dissociation process,and inhibitors dissociate from binding site moving range from 0 to 36Å, which is divided into six window,each 6-Å wide,but in the ABF output .pmf file, the value of pmf is too large,I try many times, there still exist questions.Here is one of my configures.
# Force-Field Parameters
exclude scaled1-4
1-4scaling 1.0
cutoff 12.
switching on
switchdist 10.
pairlistdist 13.5
# Integrator Parameters
timestep 1.0 ;# 2fs/step (only if needed to finish quickly)
rigidBonds water ;# needed for 2fs steps
nonbondedFreq 2
fullElectFrequency 4
stepspercycle 20
# Constant Temperature Control
langevin on ;# do langevin dynamicsgmail.google.com
langevinDamping 1 ;# damping coefficient (gamma) of 5/ps
langevinTemp $temperature
langevinHydrogen off ;# don't couple langevin bath to hydrogens
wrapAll on
# PME (for full-system periodic electrostatics)
PME yes
PMEGridSpacing 1.0
# Constant Pressure Control (variable volume)
useGroupPressure no ;# needed for rigidBonds
useFlexibleCell no
useConstantArea no

langevinPiston on
langevinPistonTarget 1.01325 ;# in bar -> 1 atm
langevinPistonPeriod 100.
langevinPistonDecay 50.
langevinPistonTemp $temperature
# Output
outputName win1
restartfreq 500 ;# 1000steps = every 1ps
dcdfreq 500
xstFreq 500
outputEnergies 500
outputPressure 500
colvars on
colvarsConfig restrain1.in
# Minimization
#minimize 500
#reinitvels $temperature
run 1500000 ;#

And here is my restrain1.in
colvarsTrajFrequency 500
colvarsRestartFrequency 500
colvar {
   name Translocation

   width 0.1

   lowerboundary 0.0
   upperboundary 6.0

   lowerwallconstant 100.0
   upperwallconstant 100.0

   distanceZ {
      main {
         atomnumbers { the atoms of ligand }
      }
      ref {
         atomnumbers { the atoms of protein and name CA
        }
      }
      axis ( 0.0, 0.0, 1.0 )
   }
}

abf {
  colvars Translocation
  fullSamples 1000
}

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