C.I.=n

Use the n orbitals bracketing the SCF HOMO, possibly after MO reordering using RECLAS(n,m), as the CI-active MOs in a CAS-CI calculation. The number of occupied CI-active MOs will be n / 2 + 1 if n is odd and n / 2 if n is even. All of the partially occupied MOs should be included in the active space.

C.I.(n,m)

Use orbitals n through m, possibly after MO reordering using RECLAS(n,m), as the CI-active MOs in a CAS-CI calculation. All of the partially occupied MOs should be included in the active space.

See Chapter 11, Configuration Interaction for a more complete discussion of Ampac’s CI capability.

Abbreviation:

none

Requires:

none

Implied by:

BIRADICAL, TRIPLET, QUARTET, EXCITED, OPEN(a, b),

Default value:

None. The manifold of MOs must be specified by the parameters “n” or “(m,n)”.

Input File (ci/ci_1.dat) :

am1 c.i.=2 cistate=3 cimax=100 singlet t=auto truste lforce bonds   
D2h Ethylene, AM1/CI,  HOMO LUMO Active, S0 (Singlet Ground State)
Opt+LowFreq, Active MOs and Bonds, Calc 3 Lowest States
 C              0.000000  0    0.000000  0    0.000000  0    0    0    0
 C              1.325916  1    0.000000  0    0.000000  0    1    0    0
 H              1.098266  1  122.715971  1    0.000000  0    1    2    0
 H              1.098266  1  122.715971  1 -180.000000  1    1    2    3
 H              1.098266  1  122.715971  1    0.000000  1    2    1    4
 H              1.098266  1  122.715971  1  180.000000  1    2    1    4
 0              0.000000  0    0.000000  0    0.000000  0    0    0    0
			

The keyword line requests C.I.=2. This means that the two MOs bracketing the occupied/virtual MO space are used: Figure A.1. C.I. Active Space Definition The same effect could be achieved using the alternate keyword C.I.=(6,7). This form of the C.I. keyword exactly specifies the range of MOs by number.