# [molpro-user] CI vectors, single vs. multiple state calcs

Terry Frankcombe tjf at rsc.anu.edu.au
Thu Mar 17 06:32:39 GMT 2011

```Hi folks

I'm doing what one might describe as CAS-CI in a (14,9) active space of
a large system, using Multi.  The orbitals come from a previous CASSCF
calculation.  I don't understand the results I get for doing a 2 state
calculation.

The two commands (in two different jobs, all other aspects being
identical) are:

{CASSCF; occ 67; closed 58; WF 130 1 2; dont orbital}
{CASSCF; occ 67; closed 58; WF 130 1 2; state 2; dont orbital}

The jobs run fine.  The ground state energy is identical in each case
(and identical to the energy from the CASSCF calculation that the
orbitals come from, as expected).  However, for the CI vectors I get:

CI vector
=========

222222aa0      0.9713361
222220aa2     -0.2062039

for the single state calc and

CI vector
=========

222222aa0      0.8989227   0.2567884
22222a2a0     -0.2150793   0.6329933
2222220aa     -0.2237106   0.4707357
22222a0a2      0.0532983  -0.2444110
2222202aa      0.0534625  -0.2372961
222222a0a      0.0722705  -0.2227077
22222abaa     -0.1444124  -0.1890428
222220aa2     -0.1682664  -0.0702741
22222aa20      0.0920977  -0.1629586
22222baaa      0.0944303   0.1467891
22222aaab      0.0683397   0.1165439
22222aa02     -0.0352542   0.0965585
22222a02a      0.0491501   0.0911501
222220a2a     -0.0008757   0.0870140
22222aaba     -0.0183576  -0.0742902
22222a20a     -0.0611334  -0.0626342
2222a22a0      0.0012538   0.0506651

for the 2 state calc.

Why are the two CI vectors for the ground state so different?

As I understand things, the CI vector is essentially the eigenvector of
a matrix which should be the same in both cases.  The energy calculated
for the second state is well separated.  Can anyone help me understand
what is going on here?

Regards
Terry

--
Dr. Terry Frankcombe
Research School of Chemistry, Australian National University
Ph: (+61) 0417 163 509    Skype: terry.frankcombe

```