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Re^2: Number of states in XMCQDPT2

Dear Igor,

I thank you for your answer, but I think that the problem lies elsewhere.
At the CAS level of theory I calculate singlets and triplets together. At the XMCQDPT2 I have TWO DIFFERENT calculations with TWO DIFFERENT effective Hamiltonians (for singlets and for triplets).
For example, if I take 10 and 10 states for singlets and triplets, I have for singlets:

*** XMC-QDPT2 ENERGIES ***
-----------------------------------------------------------------------
STATE 1ST ORDER 2ND ORDER
1 E(MCSCF)= -261.677105329713 E(MP2)= -262.669376620520
2 E(MCSCF)= -261.424716215710 E(MP2)= -262.666212340027
3 E(MCSCF)= -261.407702388902 E(MP2)= -262.648775553937
4 E(MCSCF)= -261.397971587503 E(MP2)= -262.642175973039
5 E(MCSCF)= -261.357555431463 E(MP2)= -262.557674735242
6 E(MCSCF)= -261.350462737843 E(MP2)= -262.483099692591
7 E(MCSCF)= -261.287008744978 E(MP2)= -262.431768066747
8 E(MCSCF)= -261.245424936527 E(MP2)= -262.413558691544
9 E(MCSCF)= -261.177968460496 E(MP2)= -262.401800020580
10 E(MCSCF)= -261.076974499620 E(MP2)= -262.393379265201
-----------------------------------------------------------------------

and for triplets:

*** XMC-QDPT2 ENERGIES ***
-----------------------------------------------------------------------
STATE 1ST ORDER 2ND ORDER
1 E(MCSCF)= -261.677467336572 E(MP2)= -262.650249860133
2 E(MCSCF)= -261.422736915199 E(MP2)= -262.648363483054
3 E(MCSCF)= -261.412278358189 E(MP2)= -262.647654388601
4 E(MCSCF)= -261.379098420900 E(MP2)= -262.641941065948
5 E(MCSCF)= -261.371330821571 E(MP2)= -262.556120121286
6 E(MCSCF)= -261.352101462186 E(MP2)= -262.430043338552
7 E(MCSCF)= -261.350894460654 E(MP2)= -262.429204328369
8 E(MCSCF)= -261.285325773895 E(MP2)= -262.413817400139
9 E(MCSCF)= -261.281298497540 E(MP2)= -262.407448792218
10 E(MCSCF)= -261.245207039554 E(MP2)= -262.396032593288
-----------------------------------------------------------------------

One can see that singlets and triplets lie in the different energy intervals, and I think that their contributions will be different.

For 30 and 30 states I have for singlets:

*** XMC-QDPT2 ENERGIES ***
-----------------------------------------------------------------------
STATE 1ST ORDER 2ND ORDER
1 E(MCSCF)= -261.677105329716 E(MP2)= -262.664827084210
2 E(MCSCF)= -261.424716215681 E(MP2)= -262.655108390912
3 E(MCSCF)= -261.407702389013 E(MP2)= -262.648871226260
4 E(MCSCF)= -261.397971587331 E(MP2)= -262.647641207390
5 E(MCSCF)= -261.357555431425 E(MP2)= -262.562002285147
6 E(MCSCF)= -261.350462737544 E(MP2)= -262.521468427837
7 E(MCSCF)= -261.287008744553 E(MP2)= -262.516814152587
8 E(MCSCF)= -261.245424936052 E(MP2)= -262.515688777728
9 E(MCSCF)= -261.177968460058 E(MP2)= -262.485727816582
10 E(MCSCF)= -261.076974499547 E(MP2)= -262.448472021454
11 E(MCSCF)= -261.071636924763 E(MP2)= -262.445527831057
12 E(MCSCF)= -261.061965988333 E(MP2)= -262.426980938173
13 E(MCSCF)= -261.061867648851 E(MP2)= -262.425780165295
14 E(MCSCF)= -261.058318432591 E(MP2)= -262.409979543733
15 E(MCSCF)= -260.947131439454 E(MP2)= -262.363605462445
16 E(MCSCF)= -260.939212649675 E(MP2)= -262.351319907394
17 E(MCSCF)= -260.937331966072 E(MP2)= -262.349316225763
18 E(MCSCF)= -260.900825307545 E(MP2)= -262.322552390167
19 E(MCSCF)= -260.900287274093 E(MP2)= -262.296210503329
20 E(MCSCF)= -260.882238086740 E(MP2)= -262.294632829723
21 E(MCSCF)= -260.866868419423 E(MP2)= -262.290450640511
22 E(MCSCF)= -260.863521956935 E(MP2)= -262.281366420658
23 E(MCSCF)= -260.862570729350 E(MP2)= -262.272658271511
24 E(MCSCF)= -260.846913749707 E(MP2)= -262.247134701686
25 E(MCSCF)= -260.819718841643 E(MP2)= -262.240637702006
26 E(MCSCF)= -260.799447977765 E(MP2)= -262.233250085423
27 E(MCSCF)= -260.797853874460 E(MP2)= -262.163451256534
28 E(MCSCF)= -260.765642203021 E(MP2)= -262.144550793186
29 E(MCSCF)= -260.758728140288 E(MP2)= -262.080540322113
30 E(MCSCF)= -260.756647137717 E(MP2)= -262.079221112841
-----------------------------------------------------------------------

and for triplets:

*** XMC-QDPT2 ENERGIES ***
-----------------------------------------------------------------------
STATE 1ST ORDER 2ND ORDER
1 E(MCSCF)= -261.677467336573 E(MP2)= -262.654083846240
2 E(MCSCF)= -261.422736915806 E(MP2)= -262.653265539279
3 E(MCSCF)= -261.412278358707 E(MP2)= -262.648304114864
4 E(MCSCF)= -261.379098421442 E(MP2)= -262.648127316962
5 E(MCSCF)= -261.371330822110 E(MP2)= -262.584515910929
6 E(MCSCF)= -261.352101463680 E(MP2)= -262.558824510546
7 E(MCSCF)= -261.350894462307 E(MP2)= -262.436002170858
8 E(MCSCF)= -261.285325775641 E(MP2)= -262.428495934141
9 E(MCSCF)= -261.281298499281 E(MP2)= -262.426761523750
10 E(MCSCF)= -261.245207041357 E(MP2)= -262.421963057847
11 E(MCSCF)= -261.185251020882 E(MP2)= -262.413996783130
12 E(MCSCF)= -261.099741312200 E(MP2)= -262.401036874001
13 E(MCSCF)= -261.095932349753 E(MP2)= -262.372825498208
14 E(MCSCF)= -261.095199811925 E(MP2)= -262.363547305445
15 E(MCSCF)= -261.077182795536 E(MP2)= -262.345708355947
16 E(MCSCF)= -261.045831371041 E(MP2)= -262.341998919423
17 E(MCSCF)= -261.037001604898 E(MP2)= -262.338765683535
18 E(MCSCF)= -260.986096084652 E(MP2)= -262.336175193009
19 E(MCSCF)= -260.970504809476 E(MP2)= -262.326520191372
20 E(MCSCF)= -260.953834738864 E(MP2)= -262.302975938659
21 E(MCSCF)= -260.930468059888 E(MP2)= -262.300922500423
22 E(MCSCF)= -260.927506378889 E(MP2)= -262.289594157038
23 E(MCSCF)= -260.902625698348 E(MP2)= -262.277853276837
24 E(MCSCF)= -260.878635540109 E(MP2)= -262.268828319223
25 E(MCSCF)= -260.870555344468 E(MP2)= -262.266066055734
26 E(MCSCF)= -260.866711639703 E(MP2)= -262.257206346321
27 E(MCSCF)= -260.863948383487 E(MP2)= -262.172040193340
28 E(MCSCF)= -260.861468622304 E(MP2)= -262.144226911284
29 E(MCSCF)= -260.806654554042 E(MP2)= -262.142572031784
30 E(MCSCF)= -260.805557844229 E(MP2)= -262.113701530678
-----------------------------------------------------------------------

At CAS I get E(triplet)-E(singlet) = -80 cm-1;
at CAS/XMCQDPT2(10,10) deltaE = 4198 cm-1;
at CAS/XMCQDPT2(20,20) deltaE = 2778 cm-1;
at CAS/XMCQDPT2(30,30) deltaE = 2357 cm-1.

How many triplets and singlets should I take in the XMCQDPT2 procedure: the same and very large numbers or the different numbers but in the same energy intervals?

Kind regards,
Maksim Shundalau.

On Sat Dec 24 '16 9:00pm, Igor Polyakov wrote
---------------------------------------------
>Hello, Maksim

>I'm not Alex, but I'll try to help. First of all, CASSCF state order is not guaranteed to be the correct one=)
>Larger effective Hamiltonian dimension should yield more correct results, however for big systems it is simply impractical (high computational effort) to calculate Heff for more than 10-20 states. 2x2 seems to be a bit extreme in the low end because higher states (up to 5 or even more sometimes) can be of influence to the lowest ones. I would recommend to conduct a single large calculation to see the "EIGENVECTORS OF THE EFFECTIVE HAMILTONIAN".
>For example for one of my systems:
> 1 2 3 4 5

> *******************************************************

> 1 -0.996755 -0.063006 -0.025667 0.000488 0.007272
> 2 0.068939 -0.930901 -0.324050 0.023948 0.052243
> 3 0.002769 0.257066 -0.672227 0.680566 -0.104661
> 4 0.004256 0.225480 -0.647910 -0.704316 0.166305
> 5 0.013621 0.100592 0.148076 0.039046 0.262885
> 6 -0.004291 -0.005923 -0.014240 -0.189029 -0.930557
> 7 -0.005277 0.019798 0.006718 -0.032537 0.111529
> 8 0.036419 -0.043997 -0.013186 -0.042064 -0.102410
> 9 -0.008000 -0.005780 0.016341 0.009414 0.020153
> 10 -0.008890 0.003653 0.006373 -0.004601 -0.015154

>This means that to correctly describe state 3 it is crucial to include state 4. This can also be seen in the CAS-CI states, states 3 and 4 share some large weighted CSF-S

>Best regards, Igor

>On Fri Dec 23 '16 5:37pm, Maksim Shundalau wrote
>------------------------------------------------
>>Dear Alex,
>>
>>
>>Let's pretend that I calculated two lower states (triplet and singlet) of transient molecule (or radical) at the CASSCF level of theory. I get triplet as a ground state and singlet is only a few tens of cm-1 higher than the triplet.
>>How many triplets and singlets should I take in the XMCQDPT2 procedure to get the same sequence of states and trust the results? If I take 2 and 2 (or 10 and 10), I have triplet higher than singlet. Should I take 3 and 2 (or 5 and 2, for example) for triplet and singlet, respectively?
>>
>>
>>Kind regards,
>>Maksim Shundalau.
>>

Mon Dec 26 '16 1:18pm

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