Potential Energy Surfaces

surface

The surface command allows the systematic exploration of a potential energy surface, based on a regular grid in the hyperspace defined by a set of internal coordinates. Any type of calculation on the molecule that can generate an energy may be used.

Argument	Argument type	Mandatory	Default	To specify
zmatrix=	Zmatrix tag	yes	none	specification of geometry and optimisation variables
theory=	string	yes	none	what type of calculation to perform for energy and gradient
result=	Field tag	no	surface.grid	field object to hold grid of energy values
mode=	keyword	no	rigid	what energy minimisation at each point (rigid, relax, opt)
control=	Tcl List	yes	-	control data

The surface is defined by the control argument, a Tcl List of control records. Each record controls one internal coordinate (z-matrix) parameter, and consists of four fields.

  name #pts start step

name indicates the name of the parameter, as specified in the z-matrix.

#pts is the number of steps to take in the parameter value.

start is the value of the parameter at the first point.

step is the increment to apply to the parameter.

The mode= option to the surface command determines the action taken at each step. The default action (rigid) is simply to evaluate the energy at the point obtained by substituting the variable values into the z-matrix. If mode=relax, any variables in the z-matrix specification that are not part of the definition of the hypersurface under study will be adjusted to minimise the energy (using newopt/zopt). If mode=opt is requested, all variables are optimised. In this case, the procedure is best described as a conformational search.

The variables are stepped in the opposite order to that in which they are specified. As an example the surface command:

surface theory=gamess : {listing=gamess.out } \
 result=test1.grid  zmatrix=z control= {
{ oh  5 1.5  0.05 }
{ hoh 3 90.0 5.0  }
}

will perform GAMESS-UK calculations in the order :

oh=1.5, hoh=90.0

oh=1.5, hoh=95.0

oh=1.5, hoh=100.0

oh=1.55, hoh=90.0 etc.

oh=1.75, hoh=100.0

ir_surface

The ir_surface command allows the systematic exploration of a potential energy surface, based on a regular grid in the hyperspace defined by a set of internal coordinates for use in vibrational calculations. Any type of calculation on the molecule that can generate an energy and dipole may be used.

Argument	Argument type	Mandatory	Default	To specify
zmatrix=	Zmatrix tag	yes	none	specification of geometry and optimisation variables
theory=	string	yes	none	what type of calculation to perform for energy and gradient
result=	field	-	-	field object to hold grid of energy values
restart=	keyword	-	-	restart option
coord_list=	string	-	-	list of atom-numbers to be included in datafile
datafile=	string	-	-	file to hold coordinates, energies, and dipole moments as input for vibrational code
control=	Tcl List	-	-	control data

The surface is defined as for the surface command. The datafile will contain information to go into the input-file for E.L. Meijer's vibrational wave-function solver.