Learn how to ask questions correctly

Thomas

thomaspijper@hotmail.com

Dear Alex, dear Firefly-ers,

First of all, many thanks for the post on (X)MCQDPT earlier this month ( http://classic.chem.msu.su/cgi-bin/ceilidh.exe/gran/gamess/forum/?C35e9ea936bHW-7650-1219+00.htm ). It has been of great help to understand this technique and apply it to some smaller molecules. However, for the system I’m currently investigating I would like to ask for some additional information.

For the system under investigation I’m interested in finding the energies for the 3 lowest states. The system has 4 pi bonds and 2 lone pairs which are in conjugation with the pi system, so I’ve opted for a (12,10) active space which includes all p orbitals, with state averaging over the 3 lowest states. I then did a XMCQDPT2 calculation with the following parameters:

$XMCQDPT NSTATE=15 EDSHFT=0.02 IROT=1 THRGEN=1D-10 WSTATE(1)=1,1,1,-0 AVECOE(1)=1,1,1,-0 $END

However, the results are a bit surprising when I look at the eigenvectors of the effective Hamiltonian (see attachment for full input and output files):

1 2 3 *********************************** 1 0.979176 0.088076 -0.026794 2 0.035958 0.059822 -0.016755 3 -0.035267 0.704873 0.694772 4 0.010869 0.094671 0.009798 5 0.129268 0.135014 -0.201877 6 0.033920 0.143020 -0.159014 7 0.014135 0.021763 -0.020772 8 0.001207 0.004650 -0.018419 9 -0.048716 0.049059 -0.021054 10 -0.085162 0.248572 -0.207512 11 -0.056139 0.282944 -0.224556 12 0.054204 -0.289349 0.328600 13 -0.066811 0.447878 -0.487557 14 0.016651 -0.100756 0.093465 15 0.006428 -0.070395 -0.032100

Apparently, the CASSCF states 10 till 13 contribute significantly to XMCQDPT states 2 and 3. My question is: is it common for high-lying states to be so important? Or does it rather show a problem with the underlying CASSCF states?

Then there is a second question I would like to ask. If I were to proceed by including CASSCF states 10-13 (as well as states 5 and 6 which seem to be of importance as well) in both the SA-CASSCF as well as the XMCQDPT part of the calculation, I would write the following input:

$DET NSTATE=40 ITERMX=400 WSTATE(1)=1,1,1,0,1,1,0,0,0,1,1,1,1 $END $XMCQDPT NSTATE=20 EDSHFT=0.02 IROT=1 THRGEN=1D-10 WSTATE(1)=1,1,1,0,1,1,0,0,0,1,1,1,1,-0 AVECOE(1)=1,1,1,0,1,1,0,0,0,1,1,1,1,-0 $END

However, this gives me problems during the CI optimization: after many iterations, one or more states become unconverged and will not converge again:

5 -1372.2196226568 0.00000114 5 -1372.2077781435 0.00017627 5 -1372.2072391615 0.00525372 5 -1372.2039774568 0.00568757 Warning - some CI states may have just been missed! -1 CONVERGED CI STATE(S) HAVE BECOME UNCONVERGED, NOW WORKING ON 3 STATES. After a few more iterations: 73 -3820.2279388183 30217.75359972 73 -3677.7641825114 28409.89326395 73 -2930.8951122879 15383.10968857 73 -2905.6192085034 14967.16114983 73 -2821.9694978003 14105.86660842 73 -1372.4833177907 0.00000041 73 -1372.4258925356 0.00000015 73 -1372.3874360397 0.00000021 73 -1372.3748222301 0.00000020 73 -1372.3321312588 0.00000017 73 -1372.2919746805 0.00000020 73 -1372.2521978693 0.00000018

I encounter this problem quite often for large values of NSTATE (see my other attached input and output files for an example). My question is: how does one solve this problem? I tried increasing the accuracy of the calculation (ICUT=10, INTTYP=HONDO, tighter convergence criteria), but this didn’t help.

Many thanks in advance for your help.

Kind regards,

Thom

Mon Dec 20 '10 4:06pm

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