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Pages: 1

#1 2016-04-24 09:30:17

Tapan
Member
Registered: 2016-04-24
Posts: 6

Nitrogen Dissociation Energy

As an exercise, I am trying to calculate nitrogen dissociation energy.  I have written a code to get the potential energy vs bond distance.
The following is my code for RASSCF program for one of the configuration:

&GATEWAY
coord
2
N2 geometry
N     -0.700000000000      0.000000000000      0.000000000000
N      0.000000000000      0.000000000000      0.000000000000
basis = aug-cc-PVTZ
group = NoSym
&SEWARD
&RASSCF
Spin = 1; Nactel = 6 0 0; Inactive = 4; Ras2 = 6
&CASPT2
MAXIter=500

Unfortunately, the answer that I get for the dissociation energy(potential at the minimum wrt potential when intermolecular distance is large) is 160kcal/mol, way off from the experimental value(228.7). I have changed the Nactel-Ras2 and basis set a few times but not to any success.


Please suggest where exactly am I going wrong

Last edited by Tapan (2016-04-24 09:38:59)

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#2 2016-04-25 14:50:17

Ignacio
Administrator
From: Uppsala
Registered: 2015-11-03
Posts: 1,079

Re: Nitrogen Dissociation Energy

Have you checked the orbitals to make sure the active space is correct? It's not only about the number of orbitals (RAS2), but also their nature.

And what is a "large" distance? Are you sure you are getting the asymptotic limit of the energy?

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#3 2016-04-28 13:57:18

Tapan
Member
Registered: 2016-04-24
Posts: 6

Re: Nitrogen Dissociation Energy

Thanks for the repy

I find that for a similar configuration with small difference in the interatomic distance, I get the correct dissociation energy.

Ignacio wrote:

Have you checked the orbitals to make sure the active space is correct? It's not only about the number of orbitals (RAS2), but also their nature.


How to check if the active space is correct? And as you said its not only about RAS2, but also the nature; I can relate to what you are explaining but still not getting what should I do

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#4 2016-04-28 14:04:59

Tapan
Member
Registered: 2016-04-24
Posts: 6

Re: Nitrogen Dissociation Energy

Essentially my main problem is to get an N3 PES.... For such a surface, the following 2 codes denote 2 configurations:

&GATEWAY
coord
3
N3 geometry
N               -4.50                0.00                0.00
N                0.00                0.00                0.00
N                3.88                0.41                0.00
basis = aug-cc-PVTZ
group = NoSym
&SEWARD
&RASSCF
Spin = 2; Nactel = 9 0 0; Inactive = 6; Ras2 = 9
LEVShft = 1.0
&CASPT2
MAXIter=500
&GATEWAY
coord
3
N3 geometry
N               -4.50                0.00                0.00
N                0.00                0.00                0.00
N                4.18                0.44                0.00
basis = aug-cc-PVTZ
group = NoSym
&SEWARD
&RASSCF
Spin = 2; Nactel = 9 0 0; Inactive = 6; Ras2 = 9
&CASPT2
MAXIter=500


As you can notice that all three atoms are far away from each other(dissociated state) and should give similar CASPT2 energy. The second case is where the atoms are separated by more interatomic distance. However, for the two cases I get -163.51271022 A.U. and -163.42372505 A.U. respectively. Where exactly am I going wrong

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#5 2016-04-29 08:29:03

Tapan
Member
Registered: 2016-04-24
Posts: 6

Re: Nitrogen Dissociation Energy

I have observed that few people are facing a similar problem:
http://www.molcas.org/molcas/wwwboard/m … /1309.html

As stated in the question, even I get crazy occupancy of the orbitals. I tried changing SDAV,TIGHt(THREN and THFACT) values but to no success. Unfortunately, the link has no follow up. I am changing few things... In case I come up with any solution or clue.... I will post it

Last edited by Tapan (2016-04-29 08:34:56)

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#6 2016-04-29 10:25:41

Ignacio
Administrator
From: Uppsala
Registered: 2015-11-03
Posts: 1,079

Re: Nitrogen Dissociation Energy

Tapan wrote:

How to check if the active space is correct? And as you said its not only about RAS2, but also the nature; I can relate to what you are explaining but still not getting what should I do

You have to view the orbitals (with molden, or luscus, or gv, possibly using GRID_IT), and make sure the active orbitals in the CASSCF are the ones you want (sigma, sigma*, pi, pi*, I guess). By default, the orbitals will be simply sorted by energy, the first 4 will be inactive and the next 6 will be active. If you need to change this, you can either use the ALTER keyword or modify the *Orb file used as input (see "#INDEX" at the end of the file, and put "i", "2", "s" where appropriate). The best idea is using the final orbitals of one point (*.RasOrb) as initial orbitals for the next one (FILE keyword).

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#7 2016-05-01 18:04:03

Tapan
Member
Registered: 2016-04-24
Posts: 6

Re: Nitrogen Dissociation Energy

The orbitals looks fine, but the weight and coefficients of the configuration are improper... For the first case:

 CI COEFFICIENTS LARGER THAN  0.50D-01
  Occupation of active orbitals, and spin coupling
  of open shells. (u,d: Spin up or down).
  SGUGA info is (Midvert:IsyUp:UpperWalk/LowerWalk)
   Conf   SGUGA info Occupation       Coef       Weight
     69 ( 3:1:  4/  1) 222uu000d         0.054727         0.002995
    188 ( 4:1:  3/  6) 22uduud00         0.185916         0.034565
    208 ( 4:1:  7/  7) 2u2duu0d0        -0.182891         0.033449
    230 ( 4:1: 13/  8) u22duu00d         0.180597         0.032615
    332 ( 4:1:  3/ 15) 22uudud00        -0.109669         0.012027
    352 ( 4:1:  7/ 16) 2u2udu0d0         0.103557         0.010724
    374 ( 4:1: 13/ 17) u22udu00d        -0.104342         0.010887
   1746 ( 6:1:  1/  1) 22uuudd00         0.076335         0.005827
   1753 ( 6:1:  2/  2) 2u2uud0d0        -0.073007         0.005330
   1761 ( 6:1:  4/  3) u22uud00d         0.069567         0.004840
   2037 ( 7:1: 16/ 10) 220uu020d        -0.054358         0.002955
   2114 ( 7:1: 21/ 13) 202uu002d        -0.054360         0.002955
   2154 ( 7:1: 13/ 15) 022uu200d        -0.053230         0.002833
   3800 ( 8:1:  5/ 27) 2u0duu2d0        -0.181645         0.032995
   3849 ( 8:1: 19/ 28) u20duu20d         0.179391         0.032181
   3873 ( 8:1:  8/ 29) 20uduud20         0.184622         0.034085
   3914 ( 8:1: 14/ 30) ududuuddu        -0.090207         0.008137
   3922 ( 8:1: 22/ 30) ududuudud        -0.157053         0.024666
   3964 ( 8:1: 29/ 31) 02uduud02         0.177865         0.031636
   3984 ( 8:1: 14/ 32) uudduuddu         0.053256         0.002836
   3994 ( 8:1: 24/ 32) uudduuudd        -0.166914         0.027860
   4030 ( 8:1: 25/ 33) u02duu02d         0.179363         0.032171
   4073 ( 8:1: 33/ 34) 0u2duu0d2        -0.174965         0.030613
   4395 ( 8:1:  5/ 44) 2u0udu2d0         0.102849         0.010578
   4444 ( 8:1: 19/ 45) u20udu20d        -0.103642         0.010742
   4468 ( 8:1:  8/ 46) 20uudud20        -0.108908         0.011861
   4509 ( 8:1: 14/ 47) uduududdu         0.054265         0.002945
   4517 ( 8:1: 22/ 47) uduududud         0.092036         0.008471
   4559 ( 8:1: 29/ 48) 02uudud02        -0.104919         0.011008
   4589 ( 8:1: 24/ 49) uududuudd         0.095481         0.009117
   4625 ( 8:1: 25/ 50) u02udu02d        -0.103631         0.010739
   4668 ( 8:1: 33/ 51) 0u2udu0d2         0.099071         0.009815
   6644 (11:1:  2/  8) 2u0uud2d0        -0.072508         0.005257
   6664 (11:1:  6/  9) u20uud20d         0.069102         0.004775
   6677 (11:1:  3/ 10) 20uuudd20         0.075805         0.005746
   6697 (11:1:  7/ 11) uduuuddud        -0.065267         0.004260
   6720 (11:1: 14/ 12) 02uuudd02         0.073049         0.005336
   6731 (11:1:  9/ 13) uuduududd        -0.065452         0.004284
   6750 (11:1: 12/ 14) u02uud02d         0.069093         0.004774
   6769 (11:1: 15/ 15) 0u2uud0d2        -0.069863         0.004881
   6780 (11:1: 10/ 16) uuuduuddd        -0.085333         0.007282
   6844 (11:1: 10/ 20) uuuududdd         0.066201         0.004383
   7481 (12:1: 15/ 24) 200uu022d         0.053993         0.002915
   7521 (12:1:  7/ 26) 020uu220d         0.052871         0.002795
   7598 (12:1: 12/ 29) 002uu202d         0.052858         0.002794
   8417 (13:1:  7/ 27) u00duu22d         0.178161         0.031741
   8438 (13:1: 12/ 28) 0u0duu2d2        -0.173815         0.030212
   8457 (13:1: 15/ 29) 00uduud22         0.176666         0.031211
   8529 (13:1:  7/ 34) u00udu22d        -0.102934         0.010595
   8550 (13:1: 12/ 35) 0u0udu2d2         0.098417         0.009686
   8569 (13:1: 15/ 36) 00uudud22        -0.104214         0.010861
   8695 (15:1:  1/  1) uuuuudddd        -0.052545         0.002761
   8760 (17:1:  3/  8) u00uud22d         0.068628         0.004710
   8768 (17:1:  5/  9) 0u0uud2d2        -0.069402         0.004817
   8775 (17:1:  6/ 10) 00uuudd22         0.072558         0.005265
   8812 (18:1:  1/ 10) 000uu222d        -0.052502         0.002756

and for the second case

 CI COEFFICIENTS LARGER THAN  0.50D-01
  Occupation of active orbitals, and spin coupling
  of open shells. (u,d: Spin up or down).
  SGUGA info is (Midvert:IsyUp:UpperWalk/LowerWalk)
   Conf   SGUGA info Occupation       Coef       Weight
    204 ( 4:1:  3/  7) 2u2duud00        -0.058835         0.003462
    248 ( 4:1: 15/  9) 2202u00ud         0.051518         0.002654
    535 ( 4:1: 14/ 27) 202u20u0d         0.083171         0.006917
    832 ( 5:1:  7/  5) 22020u020         0.061319         0.003760
   1166 ( 5:1:  1/ 22) uu2dd2u00         0.056419         0.003183
   1212 ( 5:1:  7/ 24) u202du020         0.058344         0.003404
   1407 ( 5:1:  2/ 34) 20202u200        -0.062429         0.003897
   1604 ( 5:1: 19/ 43) u02d20u02         0.073701         0.005432
   1989 ( 7:1: 16/  8) 2u20u020d         0.058998         0.003481
   2258 ( 7:1: 21/ 19) 2u02u002d         0.061540         0.003787
   2661 ( 7:1: 16/ 36) 20uu2020d         0.070098         0.004914
   3066 ( 8:1:  6/  6) u2du02020        -0.057838         0.003345
   3709 ( 8:1: 19/ 24) 2020uu20d        -0.065715         0.004319
   3713 ( 8:1: 23/ 24) 2020u02ud        -0.055208         0.003048
   3856 ( 8:1: 26/ 28) u20du0u2d        -0.065600         0.004303
   4023 ( 8:1: 18/ 33) u02du2u0d         0.065755         0.004324
   4165 ( 8:1: 20/ 37) 0202u20ud         0.054571         0.002978
   4170 ( 8:1: 25/ 37) 0202uu02d         0.064732         0.004190
   5225 ( 8:1: 30/ 67) u0du20202         0.056707         0.003216
   5652 ( 9:1:  2/  8) u20d02u20        -0.074586         0.005563
   5849 ( 9:1: 19/ 17) 02020u022         0.060538         0.003665
   6044 ( 9:1: 14/ 27) u020du202        -0.057514         0.003308
   6210 ( 9:1: 20/ 35) uu0dd0u22         0.055223         0.003050
   6424 ( 9:1: 14/ 46) 00202u202        -0.059470         0.003537
   7094 (12:1: 12/  8) 02uu0202d        -0.069261         0.004797
   7449 (12:1:  7/ 23) 0u20u220d        -0.060871         0.003705
   7718 (12:1: 12/ 34) 0u02u202d        -0.057934         0.003356
   8160 (13:1:  6/ 11) 020u02u2d        -0.081743         0.006682
   8399 (13:1:  5/ 26) 0020u22ud        -0.050609         0.002561
   8441 (13:1: 15/ 28) 0u0duud22         0.056708         0.003216

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