[molpro-user] Extended Multi-State CASPT2
Alan Chien
alandc at umich.edu
Wed Jul 2 17:51:39 BST 2014
Thank you for your reply Werner, its cleared up a lot of my initial
questions.
I had actually determined that there was a difference between CORE and
FROZEN, but was still trying to figure things out a bit better.
I have a few clarification questions. Please forgive the length, but I'm
trying to be as precise as possible so that no further clarifications will
be necessary, heh.
For the CAS portion of CASPT2 (separate from the MULTI calc), the reference
determinants are generated using the orbitals defined by OCC - CLOSED.
For the PT2 portion, we have to define a space from which we can do doubles
excitations, i.e. correlate certain orbitals. This is defined as those
orbitals in CLOSED - CORE. *But how do we define where those double
excitations go to*? Do they only go to the empty orbitals that we included
in OCC? Or are they automatically allowed to be excited to any/all virtuals
(Which seems unlikely since virtuals usually make up a large portion of the
MOs).
CASPT2 (RS2) defines "active space" as both the space used to create the
CAS determinants *as well as* the orbitals which we allow to be correlated.
I find this strange as before now, I've only ever worked with CAS/RAS, and
I'm used to thinking of active spaces as just the orbital set used to
generate the set of reference determinants. Is this definition of active
space a quirk of Molpro or is it the accepted standard when discussing
CASPT2?
Finally, does RS2C treat the CORE,CLOSED,OCC cards differently when making
its definition of the "active space"? This link (which I posted earlier),
http://www.molpro.net/pipermail/molpro-user/2006-April/001759.html, seems
to suggest that it does. But I am unclear as to why that may be as the
manual states that the RS2 and RS2C programs are essentially the same, just
one is faster or has different features implemented compared to the other.
Perhaps it is just a difference in the code of each program instead of a
difference having any substantive meaning?
I understand that some of these questions I can answer myself (namely the
last one) with a couple of Molpro test jobs, and in lieu of provided
answers, I may well determine them myself.
But any help is welcome,
Alan Chien
On Wed, Jul 2, 2014 at 6:12 AM, Werner Győrffy <
gyorffy at theochem.uni-stuttgart.de> wrote:
> Dear Alan,
>
> CLOSED orbitals are doubly occupied in all reference configurations but
> excitations are allowed from them in the CASPT2 calculations if they are
> not frozen. If you want to define orbitals which are frozen (not
> correlated) in CASPT2, you should use CORE orbitals. CORE orbitals are not
> counted for the 32 orbital limitation in the rs2 program.
>
> Active orbitals in CASSCF are defined as OCC minus CLOSED orbitals.
>
> An (X)MS-CASPT2 calculation is still possible only with the rs2 program
> not with rs2c.
>
> Regards,
>
> Werner Gyorffy.
>
>
>
>
> On 07/01/2014 11:56 PM, Alan Chien wrote:
>
>> Interesting nugget of information. The example given in the multi-state
>> CASPT2 section of the manual DOES change its active space when you
>> change the numbers in the closed card.
>> So it seems that for that particular example it can recognize closed
>> input.
>>
>> Example: http://www.molpro.net/info/current/examples/lif_mr_mscaspt2.com
>> (I edited it so that it only did r=3 ang to reduce the amt of output I
>> had to look at. Also removed everything below RS2 section)
>>
>> Trying to replicate it now. In fact, been trying for a while.
>>
>>
>>
>>
>> On Tue, Jul 1, 2014 at 3:48 PM, Alan Chien <alandc at umich.edu
>> <mailto:alandc at umich.edu>> wrote:
>>
>> Dear Molpro Community,
>>
>> I was wondering if there was something wrong with my following input
>> for an extended multi-state CASPT2 calculation. My input is not
>> recognizing the CLOSED card, and so is throwing the error "TOO MANY
>> ACTIVE ORBITALS: 48 THIS VERSION ALLOWS 32." An old thread mentions
>> that I should use RS2C -
>> http://www.molpro.net/pipermail/molpro-user/2006-April/001759.html -
>> which should recognize closed orbitals.
>>
>> But it's a rather old thread, and I want XMS-CASPT2 which isn't
>> implemented for RSC2, and so I thought it worth mentioning to see if
>> they had updated the RS2 code and perhaps my input was just off. The
>> manual makes no mention of RS2 being unable to recognize the CLOSED
>> card. I also tried the same input with FROZEN and that threw the
>> same error.
>>
>> Any input welcome,
>> Alan Chien
>>
>>
>> ***,title
>> memory,400,m
>> symmetry
>> geometry={
>> S 1.9692714536 0.9837700026 0.0000000000
>> C 0.6745300892 -0.1941173367 0.0000000000
>> C 1.1941024748 -1.4906632561 0.0000000000
>> C 2.5920412491 -1.5265017306 0.0000000000
>> C 3.1677860531 -0.2809638443 0.0000000000
>> C -0.6745300892 0.1941173367 0.0000000000
>> C -1.1941024748 1.4906632561 0.0000000000
>> C -2.5920412491 1.5265017306 0.0000000000
>> C -3.1677860531 0.2809638443 0.0000000000
>> S -1.9692714536 -0.9837700026 0.0000000000
>> C -4.5811338904 -0.0064991780 0.0000000000
>> C -5.5229897499 1.0602944736 0.0000000000
>> N -6.2538051640 <tel:2538051640> 1.9321608642
>>
>> 0.0000000000
>> C 4.5811338904 0.0064991780 0.0000000000
>> C 5.5229897499 -1.0602944736 0.0000000000
>> N 6.2538051640 <tel:2538051640> -1.9321608642
>>
>> 0.0000000000
>> C 5.0766433381 1.3388671764 0.0000000000
>> N 5.4513787354 2.4133206959 <tel:4133206959>
>>
>> 0.0000000000
>> C -5.0766433381 -1.3388671764 0.0000000000
>> N -5.4513787354 -2.4133206959 <tel:4133206959>
>> 0.0000000000
>> H -3.1636666579 2.4343293653 <tel:4343293653>
>> 0.0000000000
>> H -0.5803308458 <tel:5803308458> 2.3697711304
>> 0.0000000000
>> H 0.5803308458 <tel:5803308458> -2.3697711304
>> 0.0000000000
>> H 3.1636666579 -2.4343293653 <tel:4343293653>
>>
>> 0.0000000000
>> }
>>
>> basis=6-31G*
>> hf
>> {casscf;
>> closed,31,6,30,5 !core orbs, total 72
>> occ,31,8,30,7 !active orbs, total 76
>> wf,148,1,0;state,2
>> wf,148,3,0
>> pspace,100.0
>> }
>>
>> {rs2,xms=1,mix=2;
>> state,2,2,3
>> }
>>
>>
>>
>>
>>
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