Minimizing a structure using OPTIM and AMBER9

To optimize a geometry you need four (or five, see below) files with names specified in the following list:

1. coords.inpcrd -- file with coordinates in AMBER9 format

2. coords.prmtop -- AMBER9 topology file

3. min.in - file with AMBER9 keywords describing the conditions for molecular dynamics of the studied system, e.g.:

  Minimization
  &cntrl
     imin=1, maxcyc=1, ncyc=1,
     igb=2, saltcon=0.2,
     ntx=1, ntb=0,
     cut=15.0, rgbmax=12.0, ifswitch=1
   /

4. odata -- file with OPTIM keywords specifying method of minimization, convergence criterion, etc. e.g.:

  BFGSMIN 1.0D-6
  BFGSSTEPS 10000
  UPDATES 10
  MAXERISE 1.0D-4
  AMBER9 coords.inpcrd inpcrd

If the file for the starting geometry contains three columns with x, y, z coordinates, respectively, name this file start and change the last line of mentioned above odata file into:

  AMBER9 start

You still need to have a coords.inpcrd file in the same directory or OPTIM won't run!

Files coords.inpcrd and coords.prmtop are created by LEaP (program in AMBER package). In the case of coords.prmtop, it is important to use the program perm-prmtop.py to obtain a topology file that is invariant to the permutation of chemically equivalent atoms or groups (see description of perm-prmtop.py).