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#1 2026-09-22 07:20:54
- Anugraha
- Member
- Registered: 2025-12-17
- Posts: 24
Intruder state problem
Dear Molcas developres,
I am running a CASPT2 calculation on a molecule of 34 atoms for the ground and pi pi star state with state average=2. In CASPT2 section i used the IPEA shift of 0.0 and imaginary shift of 0.2. Iam attaching the output for both states :
++ CASPT2 computation for group 1
********************************************************************************
Multi-State initialization phase begins for group 1
--------------------------------------------------------------------------------
********************************************************************************
Compute H0 matrices for state 1
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
H0 matrices have been computed.
********************************************************************************
CASPT2 EQUATION SOLUTION
--------------------------------------------------------------------------------
Total nr of CASPT2 parameters:
Before reduction: 147120531
After reduction: 147093568
Variance of |WF0>: 9.9713419736
The contributions to the second order correlation energy in atomic units.
-----------------------------------------------------------------------------------------------------------------------------
IT. VJTU VJTI ATVX AIVX VJAI BVAT BJAT BJAI TOTAL RNORM
-----------------------------------------------------------------------------------------------------------------------------
1 -0.000117 -0.004188 -0.021622 -0.142950 -0.039870 -0.042941 -0.236665 -2.048814 -2.537167 0.003581
2 -0.000119 -0.004231 -0.021735 -0.143430 -0.039963 -0.042964 -0.236757 -2.048933 -2.538131 0.000278
3 -0.000119 -0.004231 -0.021735 -0.143439 -0.039963 -0.042964 -0.236764 -2.048932 -2.538147 0.000032
4 -0.000119 -0.004231 -0.021734 -0.143437 -0.039962 -0.042964 -0.236763 -2.048931 -2.538142 0.000004
-----------------------------------------------------------------------------------------------------------------------------
FINAL CASPT2 RESULT:
Reference energy: -834.6646225709
E2 (Non-variational): -2.5381418967
Shift correction: -0.0114617216
E2 (Variational): -2.5496036183
Total energy: -837.2142261892
Residual norm: 0.0000003924
Reference weight: 0.56232
Contributions to the CASPT2 correlation energy
Active & Virtual Only: -0.0646987605
One Inactive Excited: -0.3803183944
Two Inactive Excited: -2.0931247417
++ Denominators, etc.
--------------------------------------------------------------------------------------------------------------
Report on small energy denominators, large coefficients, and large energy contributions.
CASE SYMM ACTIVE-MIX NON-ACTIVE INDICES DENOMINATOR RHS VALUE COEFFICIENT CONTRIBUTION
ATVX 2 Mu2.0001 Se2.016 0.16446750 0.00008876 -0.00020242 -0.00000002
ATVX 2 Mu2.0002 Se2.016 0.27735004 0.00002079 -0.00005411 -0.00000000
ATVX 2 Mu2.0001 Se2.017 0.17676048 -0.00024815 0.00048589 -0.00000012
ATVX 2 Mu2.0002 Se2.017 0.28964301 0.00008247 -0.00006209 -0.00000001
ATVX 2 Mu2.0001 Se2.018 0.18436255 0.00007372 -0.00015557 -0.00000001
ATVX 2 Mu2.0002 Se2.018 0.29724508 -0.00002671 0.00008128 -0.00000000
ATVX 2 Mu2.0001 Se2.019 0.22307446 0.00049866 -0.00057109 -0.00000028
ATVX 2 Mu2.0001 Se2.020 0.24566379 -0.00150156 0.00258428 -0.00000388
ATVX 2 Mu2.0001 Se2.021 0.25352261 0.00099156 -0.00187405 -0.00000186
ATVX 2 Mu2.0001 Se2.022 0.26443001 0.00134464 -0.00289140 -0.00000389
ATVX 2 Mu2.0001 Se2.023 0.27701460 -0.00029005 0.00052980 -0.00000015
ATVX 2 Mu2.0001 Se2.024 0.29303259 -0.00002871 -0.00013942 0.00000000--
++ CASPT2 computation for group 2
********************************************************************************
Multi-State initialization phase begins for group 2
--------------------------------------------------------------------------------
********************************************************************************
Compute H0 matrices for state 2
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
H0 matrices have been computed.
********************************************************************************
CASPT2 EQUATION SOLUTION
--------------------------------------------------------------------------------
Total nr of CASPT2 parameters:
Before reduction: 147120531
After reduction: 147093237
Variance of |WF0>: 9.9816542846
The contributions to the second order correlation energy in atomic units.
-----------------------------------------------------------------------------------------------------------------------------
IT. VJTU VJTI ATVX AIVX VJAI BVAT BJAT BJAI TOTAL RNORM
-----------------------------------------------------------------------------------------------------------------------------
1 -0.000245 -0.004377 -0.030462 -0.154639 -0.040314 -0.043576 -0.249608 -2.048717 -2.571937 0.003830
2 -0.000252 -0.004414 -0.030648 -0.155099 -0.040388 -0.043606 -0.249694 -2.048815 -2.572916 0.000428
3 -0.000253 -0.004415 -0.030651 -0.155121 -0.040388 -0.043605 -0.249706 -2.048815 -2.572953 0.000062
4 -0.000253 -0.004415 -0.030650 -0.155115 -0.040387 -0.043605 -0.249705 -2.048813 -2.572942 0.000010
5 -0.000253 -0.004415 -0.030650 -0.155115 -0.040387 -0.043605 -0.249704 -2.048813 -2.572941 0.000001
-----------------------------------------------------------------------------------------------------------------------------
FINAL CASPT2 RESULT:
Reference energy: -834.4670908832
E2 (Non-variational): -2.5729416160
Shift correction: -0.0144302163
E2 (Variational): -2.5873718323
Total energy: -837.0544627155
Residual norm: 0.0000002124
Reference weight: 0.54873
Contributions to the CASPT2 correlation energy
Active & Virtual Only: -0.0742548589
One Inactive Excited: -0.4050719958
Two Inactive Excited: -2.0936147613
++ Denominators, etc.
--------------------------------------------------------------------------------------------------------------
Report on small energy denominators, large coefficients, and large energy contributions.
CASE SYMM ACTIVE-MIX NON-ACTIVE INDICES DENOMINATOR RHS VALUE COEFFICIENT CONTRIBUTION
VJTU 1 Mu1.0001 In1.040 0.28826619 -0.00023808 0.00054682 -0.00000013
VJTU 1 Mu1.0001 In1.041 0.27160881 -0.00012096 0.00031980 -0.00000004
VJTU 1 Mu1.0001 In1.042 0.26373035 0.00054436 -0.00130574 -0.00000071
VJTU 1 Mu1.0001 In1.043 0.25786633 0.00049647 -0.00122700 -0.00000061
VJTU 1 Mu1.0001 In1.044 0.23124537 -0.00011624 0.00035927 -0.00000004
VJTU 1 Mu1.0001 In1.045 0.20563966 -0.00014160 0.00039057 -0.00000006
VJTU 1 Mu1.0001 In1.046 0.19157691 -0.00003328 0.00015648 -0.00000001
VJTU 1 Mu1.0001 In1.047 0.18257418 0.00001161 -0.00004071 -0.00000000
VJTU 1 Mu1.0001 In1.048 0.16579633 -0.00016593 0.00040110 -0.00000007
VJTU 1 Mu1.0001 In1.049 0.15775315 0.00006336 -0.00016799 -0.00000001
VJTU 1 Mu1.0001 In1.050 0.10953556 -0.00005837 0.00019011 -0.00000001
VJTU 1 Mu1.0001 In1.051 0.07215227 -0.00006768 0.00010926 -0.00000001
VJTU 1 Mu1.0002 In1.051 0.26433715 -0.00004682 0.00009822 -0.00000000
VJTU 1 Mu1.0003 In1.051 0.27761824 0.00000181 -0.00000569 -0.00000000
VJTU 2 Mu2.0002 In2.002 0.28595473 -0.00011096 0.00028088 -0.00000003
VJTU 2 Mu2.0002 In2.003 0.26695007 -0.00021717 0.00062262 -0.00000014
VJTU 2 Mu2.0002 In2.004 0.23524463 -0.00289273 0.00860890 -0.00002490
VJTU 2 Mu2.0002 In2.005 0.13955562 -0.00020618 0.00053011 -0.00000011
VJTU 2 Mu2.0003 In2.005 0.27710224 -0.00001438 -0.00003110 0.00000000
VJTU 2 Mu2.0002 In2.006 0.11406939 0.00030984 -0.00071436 -0.00000022
VJTU 2 Mu2.0003 In2.006 0.25161601 0.00006513 -0.00032434 -0.00000002
VJTU 2 Mu2.0002 In2.007 0.09454723 -0.00037575 0.00089308 -0.00000034
VJTU 2 Mu2.0003 In2.007 0.23209384 -0.00036545 0.00094391 -0.00000034
VJTU 2 Mu2.0004 In2.007 0.29040915 0.00023695 -0.00041696 -0.00000010
VJTU 2 Mu2.0002 In2.008 0.08825529 -0.00116927 0.00260660 -0.00000305
VJTU 2 Mu2.0003 In2.008 0.22580191 -0.00133027 0.00352419 -0.00000469
VJTU 2 Mu2.0004 In2.008 0.28411722 0.00067203 -0.00112012 -0.00000075
ATVX 1 Mu1.0001 Se1.053 0.03797839 0.00001329 -0.00001051 -0.00000000
ATVX 1 Mu1.0002 Se1.053 0.21607240 -0.00001179 0.00002632 -0.00000000
ATVX 1 Mu1.0003 Se1.053 0.21667996 -0.00000306 0.00000745 -0.00000000
ATVX 1 Mu1.0001 Se1.054 0.04753370 -0.00005124 0.00005456 -0.00000000
ATVX 1 Mu1.0002 Se1.054 0.22562772 0.00003763 -0.00008840 -0.00000000
ATVX 1 Mu1.0003 Se1.054 0.22623528 0.00000053 -0.00000158 -0.00000000
ATVX 1 Mu1.0001 Se1.055 0.05521549 0.00000190 -0.00000240 -0.00000000
ATVX 1 Mu1.0002 Se1.055 0.23330951 -0.00000154 0.00000369 -0.00000000
ATVX 1 Mu1.0003 Se1.055 0.23391707 -0.00000012 0.00000006 -0.00000000.
.
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With this how do i know intruder states are present or not. If intruder states are present which shift i have to use. (I have avoided the IPEA shift because of the paper 'The IPEA Dilemma in CASPT2').
I would be really thankful if anyone can help me to solve this issue.
Thank you
Anugraha
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#2 Yesterday 15:01:06
- Ignacio
- Administrator
- From: Uppsala
- Registered: 2015-11-03
- Posts: 1,211
Re: Intruder state problem
IPEA shift is not designed to help with intruder states. An imaginary shift fo 0.2 (or 0.1, probably) should pretty much guarantee no intruder state problems.
You may suspect intruder states if:
* The reference weight is too small. Note the reference weight (always between 0 and 1) does in general go down as the number of electrons increases, so it's best to compare different roots: the weights should be similar. How much is similar? I don't know, but if one state is 0.8 and the other is 0.2, there's definitely a problem.
* There are terms with a small denominator and a large contribution.
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