The CHARMM Interface

Introduction

The CHARMM interface allows energies and gradients to be taken from the CHARMM package which runs as an independent executable. Communication with ChemShell is via named pipes, using the CTCL procedures written by Alex Turner. In order to use the interface, it is necessary to prepare a CHARMM script that will set up the system and define all parameters needed to generate a correct energy and gradient. After running this script under control of the charmm.preinit command, CHARMM waits for each set of coordinates to be sent from ChemShell. The command charmm.shutdown is used to close down the charmm process.

charmm.preinit

Command Line Arguments

Argument Argument type Mandatory Default To specify
coords Fragment tag yes none The coordinates of the system (output)
charmm_script file yes none Control script for CHARMM
executable file no charmm Name of CHARMM executable

charmm.energy etc

Since all control information is fed to CHARMM via the charmm script, very few arguments will be fed to the energy and gradient evaluation routines (contrast with the DL_POLY interface, where all control is provided by arguments). Clearly, when the charmm interface procedures are executed arguments are used to control the input coordinates, and output energy and gradient matrices following the conventions used by all energy/gradient evaluators.

Examples

# start charmm
charmm.preinit charmm_script=test.charmm coords=charmm.c

# optimise
newopt function=copt : { theory=charmm coords=charmm.c  }

# end charmm
charmm.shutdown




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