Hi,
I want to fragment ethane as two methyl radicals. This is what I tried:
# Geometry @ PBE/cc-pVDZ w/ ORCA 3
memory 4000 mb
set {
basis jun-cc-pVDZ
reference uhf
# scf_type df
}
molecule {
0 2
H -0.97395637142895 -0.33919214271350 -0.41740669835522
H 0.78074222854571 -0.67377559545544 -0.41707405986210
H 0.19295516133507 1.01310450698540 -0.41737407148921
C 0.00003917953494 0.00004478839706 -0.00814962304354
--
0 2
C -0.00003917886785 -0.00004479102906 1.52020761150977
H -0.78074222517214 0.67377559966970 1.92913204324353
H -0.19295516553330 -1.01310450794172 1.92943206399842
H 0.97395637158652 0.33919214208754 1.92946469039835
units angstrom
symmetry c1
no_reorient
no_com
}
energy('sapt0')
Expecting a negative interaction energy, I found, to my surprise, the following:
SAPT Results
--------------------------------------------------------------------------------------------------------
Electrostatics -223.59373582 [mEh] -140.30719337 [kcal/mol] -587.04535340 [kJ/mol]
Elst10,r -223.59373582 [mEh] -140.30719337 [kcal/mol] -587.04535340 [kJ/mol]
Exchange 679.89602607 [mEh] 426.64121537 [kcal/mol] 1785.06701643 [kJ/mol]
Exch10 679.89602607 [mEh] 426.64121537 [kcal/mol] 1785.06701643 [kJ/mol]
Exch10(S^2) 338.46393219 [mEh] 212.38933286 [kcal/mol] 888.63705396 [kJ/mol]
Induction -223.53136555 [mEh] -140.26805543 [kcal/mol] -586.88160024 [kJ/mol]
Ind20,r -424.32601598 [mEh] -266.26860613 [kcal/mol] -1114.06795496 [kJ/mol]
Exch-Ind20,r 28.86291334 [mEh] 18.11175232 [kcal/mol] 75.77957898 [kJ/mol]
delta HF,r (2) 171.93173709 [mEh] 107.88879838 [kcal/mol] 451.40677574 [kJ/mol]
Dispersion -48.51926896 [mEh] -30.44630220 [kcal/mol] -127.38734064 [kJ/mol]
Disp20 -51.54141750 [mEh] -32.34272913 [kcal/mol] -135.32199165 [kJ/mol]
Exch-Disp20 3.02214855 [mEh] 1.89642692 [kcal/mol] 7.93465101 [kJ/mol]
Total HF 232.77092470 [mEh] 146.06596657 [kcal/mol] 611.14006280 [kJ/mol]
Total SAPT0 184.25165574 [mEh] 115.61966437 [kcal/mol] 483.75272215 [kJ/mol]
--------------------------------------------------------------------------------------------------------
A repulsive interaction. Can this be possibly correct? Well, I thought this could have something to do with spin:
$ grep @ etano.out
...
# supermolecule
@Spin Contamination Metric: 8.131259654E-03
@S^2 Expected: 7.500000000E-01
@S^2 Observed: 7.581312597E-01
@S Expected: 5.000000000E-01
@S Observed: 5.000000000E-01
@DF-UHF Final Energy: -39.55040227009846
This is not the multiplicity I wanted. How can I select the multiplicity of the final molecule using SAPT0? Is it even possible?
Thanks in advance,
Felipe