The GULP Interface

Introduction

This document describes the interface to GULP, as used in the shell model QM/MM implementation. The interface works by passing the input coordinate and shell positions into a standard gulp input file, and concatenating a user supplied set of gulp forcefield directives, which ChemShell does not try to intercept. It is assumed that the forcefield definition given in the file provided for GULP is appropriate for the setup of the system, with no additional changes required for QM/MM calculations.

Because it does not attempt to modify the topology generated (in contrast to the dl_poly interface that creates the DL_POLY topology) the GULP interface will ignore the following arguments conn atom_attributes atom_types atom_charges atom_pols atom_rads atom_names. For compatability these arguments are silently ignored.

As of ChemShell 3.7, the interface supports GULP v4.4.4 or later.

Command Line Arguments

Argument	Argument type	Mandatory	Default	To specify
coords=	Fragment tag	yes	none	Configuration of the system
energy=	Matrix tag	yes	none	where to store the energy
gradient=	Matrix tag	yes	none	where to store the gradient
mm_defs=	file name	yes	none	File containing the GULP directives to define the forcefield
include_qm_force=	Boolean	no	no	Whether to import the QM electrostatic forces acting on the shells
export_charge_list=	Tcl variable name	no	don't export	Variable to hold the charges on the MM centres after initialisation
gulp_keywords=	Tcl List	no	none	List of additional flags to be added to the first record of the GULP input deck. Those can also be specified in the file given at mm_defs.