frequency calculation using CASSCF and CASPT2


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Posted by Joonghan Kim on May 03, 2007 at 13:47:40:

I have some problems in frequency calculation using CASSCF and CASPT2.

First, I have performed frequency calculation using CASSCF(9,8).
The target molecule has Cs symmetry and it has two electronic states. (A' and A")
I have completed the calculation the A" state and obtained the harmonic frequencies.
However, in the calculation of the A' state, the error occured.
The output is as follows.

Process perturbation number 12
****************************************
* *
* WARNING!! *
* Elements in the E^[2] matrix small!! *
* The calculation might diverge. *
* *
* Check your active space!!!! *
* *
* Make sure degenerate orbitals do not *
* belong to different spaces. *
* Note that no LR code can handle *
* 2.0d0 occupancy in active orbitals!! *
****************************************

I have changed options (ITERATIONS and THRESHOLD in MCLR) and calculated again.
However, the results are same.
How can I do to resolve this problem.

I calculated the frequency using numerical CASPT2 calculation. (using the Slapaf program)
I have obtained only A' modes as results.
I could not obtain A" modes.
So, I calculated again using C1 symmetry.
However, I could not obtain the results.
Errors occur.
How can I obtain all modes (A' and A")?

The input file is as follows.
&SLAPAF &END
Numerical Hessian
ITERATIONS
0
End of input
>>> EndDo

The last line of the output is as follows.
FORTRAN STOP
real 0.09
user 0.07
sys 0.00
--- Stop Module: slapaf at Thu May 3 18:28:22 KST 2007 /rc= 1 ---
--- Stop Module: slapaf at Thu May 3 18:28:22 KST 2007 /rc= 1 ---
Emil command >>> enddo
--- Stop Module: auto at Thu May 3 18:28:22 KST 2007 /rc=1 ---
--- Stop Module: auto at Thu May 3 18:28:22 KST 2007 /rc=1 ---
*** The limit of loop iterations has been reached
--- Stop Module: auto at Thu May 3 18:28:22 KST 2007 /rc=1 ---
--- Stop Module: auto at Thu May 3 18:28:22 KST 2007 /rc=1 ---




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