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sanya
sanya@photonics.ru

Not exactly. After setting NSTATE=10, look carefully at the CI states (either before or after CASSCF iterations) and make sure that the state you need is among the averaged states (i.e., if you are averaging over 2 states, make sure that the state you are interested in is #1 or #2; otherwise, you should average over more states). In further runs (for example, if CASSCF has not converged in your first run), you may reduce NSTATE to a desired minimum (but leave a couple of extra states to be on the safe side). In general, the first run is done to get the idea of how many states to average (hence, you do not need to wait for CASSCF to converge), and in further runs you will set correct WSTATE and, possibly, smaller NSTATE. If your active space and/or basis set is large, excessive NSTATE may require extra disk space.

>Then, during the MCQDPT step, the effective Hamiltonian should include enough (at least 10) states in order to obtain good results.

Yes, and the size of the effective Hamiltonian does not depend on NSTATE in $DET/$DRT

>So, when trying to calculating the energy of the first excited state, the CASSCF/MCQDPT part of the input file could look like this (state-specific example):
>$DET GROUP=C1 NCORE=19 NACT=6 NELS=6 NSTATE=10 WSTATE(1)=0,1 $END
>$MCQDPT KSTATE(1)=1,1,1,1,1,1,1,1,1,1 EDSHFT=0.02 $END
>(in which KSTATE(1)=1,1,… could be also written as NSTATE=10)
>

Not quite so, again. WSTATE(1)=0,1 may cause convergence problems. It is better to set WSTATE(1)=1.0,0.1 for the first state and WSTATE(1)=0.1,1.0 for the second state. Or WSTATE(1)=1.,1. for both states.

>That leaves me with two questions about the output of a MCQDPT calculation. First, the above method gave me a list of energies:
>
>
>*** MC-QDPT2 ENERGIES ***
>-----------------------------------------------------------------------
>1 E(MCSCF)= -1365.5486114818 E(MP2)= -1367.1030309626
>2 E(MCSCF)= -1365.3205961740 E(MP2)= -1367.0468868024
>3 E(MCSCF)= -1365.2696589473 E(MP2)= -1366.9541974175
>4 E(MCSCF)= -1365.2608241655 E(MP2)= -1366.8545831671
>5 E(MCSCF)= -1365.2519965112 E(MP2)= -1366.8430834090
>6 E(MCSCF)= -1365.2308933371 E(MP2)= -1366.8176982023
>7 E(MCSCF)= -1365.2266705813 E(MP2)= -1366.7604573556
>8 E(MCSCF)= -1365.2085431094 E(MP2)= -1366.7489911227
>9 E(MCSCF)= -1365.2074885849 E(MP2)= -1366.7273932680
>10 E(MCSCF)= -1365.2018793382 E(MP2)= -1366.2020115102

>Are these energies of roots or of CI states (I'm guessing roots)?

I may be wrong, but I see no difference between the CI roots and states. And, I'm afraid, the lines you cited do not adequately show how QDPT procedure corrected (and reordered) the states. I mean that the energies are just listed in ascending order, while the character of, say, state #2 may be different in MCSCF and MCQDPT.

>Second question: the output also contained 10 sections called "Properties for the zero-order QDPT density". Here's one of them:

>WAVEFUNCTION NORMALIZATION = 1.0000000000

>ONE ELECTRON ENERGY = -4703.5993126161
>TWO ELECTRON ENERGY = 1914.3537631053
>NUCLEAR REPULSION ENERGY = 1423.7688450077
>------------------
>TOTAL ENERGY = -1365.4767045030

>ELECTRON-ELECTRON POTENTIAL ENERGY = 1914.3537631053
>NUCLEUS-ELECTRON POTENTIAL ENERGY = -6062.3804478862
>NUCLEUS-NUCLEUS POTENTIAL ENERGY = 1423.7688450077
>------------------
>TOTAL POTENTIAL ENERGY = -2724.2578397731
>TOTAL KINETIC ENERGY = 1358.7811352701
>VIRIAL RATIO (V/T) = 2.0049276289
>
>
>What exactly are these energies? They seem to be CASSCF energies, but they don't match those in the "*** MC-QDPT2 ENERGIES ***" section above.

CASSCF wavefunction is a zero-order approximation to MCQDPT. I'm not sure but I guess that this is a state-averaged CASSCF energy. What WSTATE was in the corresponding MCSCF run?