*MOLGRD

The section gives directives for control of a single point evaluation of the molecular gradient activated with .MOLGRD under **PROPERTIES.

The molecular gradient module is usually called from within the geometry optimization module.

Advanced options

.TRICK

If activated the calculation of the SL and SS two-electron integral contributions to the gradient is skipped if their contribution is estimated to be small. An “empirical” estimate of the norms of the LS and SS two-electron gradients based on the norm of the LL two-electron gradient. If deactivated all contributions to gradient are calculated and if activated then only “necessary” contributions are calculated.

Default: Deactivated.

.INTFLG

Specify what two-electron integrals to include (default: .INTFLG under **HAMILTONIAN).

.SCREEN

Screening threshold.

Default:

.SCREEN
 1.0D-17

Which means that screening is turned off by default. This is due to an enormous demand of memory.

Programmers options

.PRINT

Print level.

A print level of less than 3 gives only the total gradient. Print levels from 3+ gives individual contributions to the gradient (kinetic energy gradient, nuclear attraction gradient etc.). Print levels of 5+ print some matrices, and 10+ give massive output!

Default: Print level from **GENERAL.

.NUMGRA

Calculate the molecular gradient using numerical differentiation.

Default: Analytical evaluation if implemented.