Alex Nest
comconadin@gmail.com
>I recommend C1 point group (to allow unsymetrical occupation of orbitals in "symmetry-identical atoms", UHF (to allow unpaired alpha and unpaired beta electrons to reside in widely disparate orbitals) and "manual" construction of initial guesses using the method of Szilagyi, R. K. and Winslow, M. A. (2006) J. Comput. Chem., 27: 1385–1397 .
>You will still need a large amount of work and (especially) luck, though :-(
Do you mean that automatic SCF procudure performed by GAMESS do not result to the correct electronic structure?
As I understand (please correct me if I get wrong) if I have spin populations (alpha minus beta) like the following (for MULT=2):
ATOMIC SPIN POPULATION (ALPHA MINUS BETA)
ATOM MULL.POP. LOW.POP.
1 C -0.009151 -0.003594
2 C -0.009151 -0.003595
3 C -0.009151 -0.003595
4 S 0.104176 0.093758
5 S 0.104176 0.091590
6 S 0.104176 0.091881
7 H 0.002742 0.001566
8 H 0.002742 0.001568
9 H 0.002742 0.001573
10 H -0.003580 -0.002788
11 H -0.003580 -0.002778
12 H -0.003580 -0.002779
13 H 0.002742 0.001566
14 H 0.002742 0.001572
15 H 0.002742 0.001567
16 S -0.446735 -0.380294
17 S -0.446735 -0.378648
18 S -0.446735 -0.380551
19 S -0.675558 -0.628123
20 FE 0.908325 0.833016
21 FE 0.908325 0.833580
22 FE 0.908325 0.833509
it is incorrect because I should have ~ -4 at one Fe and ~ +4 at the another one or something like this.
Or for MULT=5 I should not get the following:
ATOMIC SPIN POPULATION (ALPHA MINUS BETA)^M
ATOM MULL.POP. LOW.POP.^M
1 C 0.000553 0.001053^M
2 C 0.000553 0.001064^M
3 C 0.000553 0.001059^M
4 S 0.019501 0.022770^M
5 S 0.019501 0.023763^M
6 S 0.019501 0.024020^M
7 H 0.000156 0.000189^M
8 H 0.000156 0.000193^M
9 H 0.000156 0.000190^M
10 H 0.000234 0.000437^M
11 H 0.000234 0.000435^M
12 H 0.000234 0.000435^M
13 H 0.000018 0.000107^M
14 H 0.000018 0.000109^M
15 H 0.000018 0.000109^M
16 S 0.084614 0.082322^M
17 S 0.084614 0.082302^M
18 S 0.084614 0.082187^M
19 S 0.169856 0.165213^M
20 FE 1.171638 1.168556^M
21 FE 1.171638 1.171346^M
22 FE 1.171638 1.172142^M
But I should obtain +5 -5 and +4 at three irons.. or like this. How can I validate that it is true? Is there some experimental results that say that spin density at iron atoms of Fe-S clusters should be such assymmetric?