Multireference Scan of Diatomic Molecules
Contents
Multireference Scan of Diatomic Molecules#
Simple Cases: H2, F2 and N2#
As mentioned in the previous article, RHF stability and UNO occupation is highly important in choosing CASSCF strategy. Let’s illustarte that by plotting \(<S^2>\) and CASNO/UNO occupation number of three simple cases.
Here we can see that
minimal CAS |
H2 |
F2 |
|
|---|---|---|---|
RHF stable, LUNO<0.02 |
(0,0) |
<= 0.6 |
<= 1.0 |
RHF stable, LUNO>0.02 |
(2,2) |
0.7 - 1.2 |
1.1 - 1.3 |
RHF unstable, LUNO>0.02 |
(2,2) |
>= 1.3 |
>= 1.4 |
minimal CAS |
N2 |
||
|---|---|---|---|
RHF stable |
(4,4) |
<= 0.6 |
|
RHF stable |
(6,6) |
0.7 - 1.2 |
|
RHF unstable |
(6,6) |
>= 1.4 |