H2 dissociation with UHF

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Lexin Ding

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Jan 13, 2022, 7:01:10 AMJan 13
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Hi everyone,

I am trying to get a symmetry-broken solution of the H2 ground state using the UHF method. In an old correspondence by Werner he suggested the following:

"
symmetry broken starting orbitals...can be obtained by first doing a rhf calculation for the triplet, and then rotating the two open-shell orbitals by 45 degrees (using ROTATE). This input does the job: geometry={x,y;h1;h2,h1,r} r=4 hf;wf,spin=2 uhf;wf,spin=0;rotate,1.1,2.1,45
"

I tried this input but it doesn't work. I assume the syntax has already been updated. I used the following input instead

"

geometry={

H1

H2 H1 r(i)}

{hf,

wf,2,1,2

}

{uhf,

wf,2,1,0,

rotate,1.1,2.1,45}

"


But the hf and uhf energy still coincide, namely the symmetry is still not broken in the uhf process. Does anyone have a solution around this? Thanks very much in advance!


Best wishes,

Lexin

Yuri Alexandre Aoto

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Jan 13, 2022, 8:16:11 AMJan 13
to Lexin Ding, molpro-user
Hi Lexin,

you need the keyword "nosym", or "nosymmetry", before the geometry to have a symmetry broken solution, otherwise symmetry is enforced by default.

yuri



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Lexin Ding

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Jan 13, 2022, 10:20:51 AMJan 13
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Thanks a lot! That worked like a charm :).

Best wishes,
Lexin

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