*CI INPUT

Purpose:

Options for a CI calculation.

.CIDENSITY

Calculate CI one-electron density matrix and natural orbital occupations after convergence.

.CINO

Generate CI natural orbitals for CI root number ISTACI, clear the SIRIUS.RST file and write the orbitals with label "NEWORB ". The ".STATE" option must be specified.

.CIROOTS

Default: NROOCI = 1
READ (LUINP,*) NROOCI
Converge the lowest NROOCI CI roots to threshold.

.DISKH2

Active two-electron MO integrals on disk (see comments below).

.MAX ITERATIONS

READ (LUINP,*) MXCIMA
Max iterations in iterative diagonalization of CI matrix (default = 20).

.STATE

Default: not specified
READ (LUINP,*) ISTACI
Alternative to ".CIROOTS". Converge root number ISTACI to threshold, converge all lower roots only to THQMIN (from the "*OPTIMIZATION" input group, see p. ).

.THRESH

Default = 1.D-05
READ (LUINP,*) THRCI
Threshold for CI energy gradient. The CI energy will be converged to approximately the square of this number.

.THRPWF

Default = 0.05D0 for electronic ground states, and 0.10D0 for excited states
READ (LUINP,*) THRPWF
Only CI coefficients greater than threshold are printed (PWF: print wave function).

.WEIGHTED RESIDUALS

Use energy weighted residuals (see comments below).

.ZEROELEMENTS

Zero small elements in CI trial vectors (see comments below).

Comments:

DISKH2: By default the CI module will attempt to place the two-electron integrals with four active indices in memory for more efficient calculation of CI sigma vectors, if memory is insufficient for this the integrals will automatically be placed on disk. The DISKH2 keyword forces the integrals always to be on disk.

WEIGHTED RESIDUALS: Normally the CI states will be converged to a residual less than the specified threshold, and this will give approximately the squared number of decimal places in the energy. Depending on the value of the energy, the eigenvectors will be converged to different accuracy. If the eigenvectors are wanted with, for instance at least 6 decimal places for property calculations, specify a threshold of 1.0D-6 and weighted residuals.

ZEROELEMENTS: an experimental option that might save time (if the CI module can use sparseness) by zeroing all elements less than 1.0D-3 times the largest element in the CI trial vector before orthonormalization against previous trial vectors. See also ".SYM CHECK" under "*OPTIMIZATION" (p. ).