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Contents 1 *TWOINT -- Two-electron integrals 1.1 .SCREEN 1.2 .ICEDIF 1.3 .THRFAC 1.4 .SOFOCK 1.5 .PRINT 1.6 .TIME 1.7 References

*TWOINT -- Two-electron integrals

This subsection gives directives for the generation of two-electron integrals.It also gives directives for the construction of Fock matrices, such as screening.

Advanced options

.SCREEN

Screening threshold for integral direct calculations of Fock matrices ^[1].

Default:

.SCREEN
 1.0D-12

Note that the screening threshold may influence the convergence. In general, the screening threshold must be about three orders of magnitude smaller than the desired norm of the electronic gradient at convergence.

Choosing a negative value for the screening turns the integral screening completely off.

.ICEDIF

Separate screening of Coulomb and exchange contributions ^[1]. Useful for fine regulation of the convergence process.

Default: Coulomb and exchange on (1 = on; off = 0).

.ICEDIF
 1 1

.THRFAC

Adjust the integral thresholds for SL and SS integrals. For conventional integral calculations only integrals above the threshold given in the basis file are written to disk. The thresholds for the SL and SS integrals are divided by the factors given here.

Default:

.THRFAC
 1.0 1.0

.SOFOCK

Do direct Fock matrix construction in symmetry-adapted basis (SO basis).

Default: Direct Fock matrix construction in AO basis using the skeleton matrix approach. This may give better screening, but is more memory intensive.

Programmers options

.PRINT

Set the print level in two-electron integral routines for the calculation of a particular shell quadruplet. The print level is changed only for the given shell quadruplet. A zero matches all shells, thus

.PRINT
 4 0 0 0 0

or just

.PRINT
 4

sets the print level to 4 for all shell quadruplets.

Use with care to avoid massive output! At print level 15 the individual integrals are printed.

.TIME

Give detailed timing for integral calculation.

References

1. ↑ ^{1.0 1.1} T. Saue, K. Fægri, T. Helgaker, and O. Gropen, Principles of direct 4-component relativistic SCF: Application to cesium auride, Mol. Phys. 91, 937 (1997) electronic version.