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Thomas

thomaspijper@hotmail.com

Dear Sanya,

First of all, thank you for your quick and informative reply.

> What does NSTATE in $MCQDPT group mean, is still unclear

> for me, but KSTATE defines, which states are to be

> included in the effective Hamiltonian. It is advisable to

> include no less than 10 states if you are interested in 2

> lowest roots. However, H_{eff} cannot include more

> states than the active space itself has; hence, for very

> small active spaces (say, CASSCF(2,2)), you should include

> all states into H_{eff}.

This part I find a bit confusing, perhaps because we're talking about both states and roots. From what I understand, both WSTATE (in $DET) and KSTATE (in $MCQDPT) refer to roots, whereas NSTATE (in $DET) refers to CI states. I assume that when you speak of "no less than 10 states", you are talking about NSTATE in $DET (NSTATE=10 or higher).

Having that said, I would like to provide the following hypothetical case to see if I got the point: the cyclization of hexatriene to cyclohexadiene. This is a 6-electron pericyclic reaction, so CASSCF(6,6) would be a good active space for this. May I ask you to comment on the following input sections which I would use for such a case? (BTW, I do understand that for bigger systems it is better to run the CASSCF part parallel and the MCQDPT part multithreaded in two separate runs).

CASSCF(6,6)/MCQDPT2 on the S_{0} PES (lowest root):

$CONTRL SCFTYP=MCSCF RUNTYP=ENERGY MPLEVL=2 INTTYP=HONDO UNITS=ANGS $END

$SYSTEM TIMLIM=300 MEMORY=15000000 MKLNP=2 $END

$P2P P2P=.True. DLB=.True. $END

$BASIS GBASIS=N21 NGAUSS=3 NDFUNC=1 $END

$MCSCF CISTEP=ALDET $END

$DET GROUP=C1 NCORE=19 NACT=6 NELS=6 NSTATE=10 WSTATE(1)=1,0 $END

$MCQDPT KSTATE(1)=1,0 EDSHFT=0.02 $END

$GUESS GUESS=MOREAD NORB=70 $END

CASSCF(6,6)/MCQDPT2 on the S_{1} PES (second root):

$CONTRL SCFTYP=MCSCF RUNTYP=ENERGY MPLEVL=2 INTTYP=HONDO UNITS=ANGS $END

$SYSTEM TIMLIM=300 MEMORY=15000000 MKLNP=2 $END

$P2P P2P=.True. DLB=.True. $END

$BASIS GBASIS=N21 NGAUSS=3 NDFUNC=1 $END

$MCSCF CISTEP=ALDET $END

$DET GROUP=C1 NCORE=19 NACT=6 NELS=6 NSTATE=10 WSTATE(1)=0,1 $END

$MCQDPT KSTATE(1)=0,1 EDSHFT=0.02 $END

$GUESS GUESS=MOREAD NORB=70 $END

For state-averaged CASSCF I would try the following:

SA-CASSCF(6,6)/MCQDPT2 on the S_{0} PES (lowest root):

$CONTRL SCFTYP=MCSCF RUNTYP=ENERGY MPLEVL=2 INTTYP=HONDO UNITS=ANGS $END

$SYSTEM TIMLIM=300 MEMORY=15000000 MKLNP=2 $END

$P2P P2P=.True. DLB=.True. $END

$BASIS GBASIS=N21 NGAUSS=3 NDFUNC=1 $END

$MCSCF CISTEP=ALDET $END

$DET GROUP=C1 NCORE=19 NACT=6 NELS=6 NSTATE=10 WSTATE(1)=1,1 $END

$MCQDPT KSTATE(1)=1,1 EDSHFT=0.02 $END

$GUESS GUESS=MOREAD NORB=70 $END

SA-CASSCF(6,6)/MCQDPT2 on the S_{1} PES (second root):

$CONTRL SCFTYP=MCSCF RUNTYP=ENERGY MPLEVL=2 INTTYP=HONDO UNITS=ANGS $END

$SYSTEM TIMLIM=300 MEMORY=15000000 MKLNP=2 $END

$P2P P2P=.True. DLB=.True. $END

$BASIS GBASIS=N21 NGAUSS=3 NDFUNC=1 $END

$MCSCF CISTEP=ALDET $END

$DET GROUP=C1 NCORE=19 NACT=6 NELS=6 NSTATE=10 WSTATE(1)=1,1 $END

$MCQDPT KSTATE(1)=1,1 EDSHFT=0.02 $END

$GUESS GUESS=MOREAD NORB=70 $END

Thank you in advance!

Kind regards,

Thom

On Mon Oct 18 '10 5:15pm, sanya wrote

-------------------------------------

>>1- What is the function of the $DRT group in the above input file? As far as I understand, the CISTEP=ALDET keyword should make the program use the Ames Lab determinant CI and read the settings in the $DET group. Doesn’t this make the $DRT group (as well as the associated $GUGEM, $GUGDM2, and $GUGDIA groups) nonfunctional?

>You are right, $DET is for ALDET CI, while $DRT is for GUGA CI and, therefore, is ignored when ALDET is used.

>>2- What is the function of the NSTATE keyword in the $MCQDPT group and what is its relation to the KSTATE keyword? At first glance, it seems that NSTATE is for the inclusion of more than one state in the MCQDPT part of the calculation, but I thought that this is what KSTATE is for. Incidentally, I have performed a few MCQDPT2 calculations with either keyword (NSTATE=2 or KSTATE(1)=1,1), but the differences in energy where negligible.

>What does NSTATE in $MCQDPT group mean, is still unclear for me, but KSTATE defines, which states are to be included in the effective Hamiltonian. It is advisable to include no less than 10 states if you are interested in 2 lowest roots. However, H_{eff} cannot include more states than the active space itself has; hence, for very small active spaces (say, CASSCF(2,2)), you should include all states into H_{eff}.

>>3- And finally, what does the IROT keyword in the $MCQDPT group do? Its function unfortunately is not described in the most up-to-date Firefly documentation as well as the current GAMESS US documentation.

>This question is for Alex, I believe :)

>In general, it is advisable to perform CASSCF calculation in parallel on as many nodes as possible (32 cores for 1000 basis functions and up to 100000 CSFs is OK), because MCQDPT can run only on one node in multi-threading mode, while CASSCF in this mode will be very slow. Next, MOREAD the OPTIMIZED ORBITALS for MCQDPT run. MCQDPT will use settings from $DET of $DRT groups, so that the input in $MCQDPT group is reduced to INORB=1 (means use of CASSCF MOs as is) KSTATE(1)=.... EDSHFT=0.02 (reasonable value of ISA energy denominator shift).

>In addition, you may use XMCQDPT (http://classic.chem.msu.su/gran/gamess/xmcqdpt.pdf;http://classic.chem.msu.su/gran/gamess/xmcqdpt.pdf;) its keywords are identical with MCQDPT. Unlike MCQDPT, XMCQDPT lacks some severe drawbacks described in http://classic.chem.msu.su/gran/gamess/mcqdpt-vs-xmcqdpt-in-O3.pdfhttp://classic.chem.msu.su/gran/gamess/mcqdpt-vs-xmcqdpt-in-O3.pdf and http://classic.chem.msu.su/gran/gamess/conic-qdpt.pdfhttp://classic.chem.msu.su/gran/gamess/conic-qdpt.pdf

*[ This message was edited on Tue Oct 19 '10 at 11:41am by the author ]*

Tue Oct 19 '10 11:41am

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