Problem RASPT2 gradient
Dear developers
I am trying to perform a geometry optimization with the RASPT2 method for a medium-sized molecule. This system corresponds to 9-cyano-10-nitroanthracene, for which I am using the following RAS space:
&RASSCF
symmetry=1;
spin=1;
nactel=20 2 2;
INACtive=54;
Ras1=8;
Ras2=4;
Ras3=8;
CIRoot= 3 3 1;
However, the program performs a couple of steps in the optimization and eventually aborts at the part where it calculates the quantities required to evaluate the RASPT2 gradient, displaying the following error message:
Solving the Lambda equation for analytic gradients
-----------------------------------------------------------------------------------------------------------------------------
IT. VJTU VJTI ATVX AIVX VJAI BVAT BJAT BJAI TOTAL RNORM
-----------------------------------------------------------------------------------------------------------------------------
SIGMA F. ICASE1,ISYM1: 1 1
**Colossal value detected in SIGMA.**
This implies that the thresholds used for linear
dependence removal must be increased.
Present values, THRSHN, THRSHS: 1.0000000000000000E-010 1.0000000000000000E-008
Use keyword THRESHOLD in input to increase these
values and then run again.
I have already changed the values of THRSHN and THRSHS using the keyword 'THRESHOLD', but the problem persists. I am not sure if I am doing something wrong or if the problem is due to numerical instability when solving the Z-vector equations. I attach the input, a geometry where the error is reproduced and the RASSCF orbital file.
I would be very grateful for your support in advance.