40.1.1 Options to select the wavefunction and energy to be optimized

By default, the last computed energy is optimized, and all commands on which the last energy calculation depends are automatically executed. For certain purposes, e.g., optimization of counter-poise corrected energies or Davdison corrected energies, the following options can be used to alter the default behaviour.

STARTCMD=command

Specifies a start command. In each geometry optimization step all input beginning with command to the current OPTG is processed. This input must not include numerical gradient or Hessian calculations. If numerical gradients are needed, these will be computed for the final energy (or specified variable) by OPTG. It is assumed that these commands have been executed before entering the OPTG program.

PROC=procname

specifies a procedure to be executed in each geometry optimization step. This must define a complete energy calculation (orbital optimization and correlation treatment), and must not include numerical gradient of Hessian calculations (numerical gradients will be computed automatically for the optimized energy or variable). However, the procedure can include the calculation of analytical gradients, for instance for counter-poise corrected optimizations in which a linear combination of several gradient calculations is needed.

VARIABLE=varname

Optimize the value of variable varname. This implies numerical gradients.