Problems obtaining g-tensor in MCSCF calculation

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cgilardoni
Posts: 1
Joined: 21 Mar 2018, 10:40
First name(s): Carmem
Last name(s): Maia Gilardoni
Affiliation: University of Groningen
Country: Netherlands

Problems obtaining g-tensor in MCSCF calculation

Post by cgilardoni » 21 Mar 2018, 11:16

I am relatively new to Dalton, so I excuse myself if I am missing something obvious. I am trying to set up a calculation in order to investigate the effect of various symmetries in the g-parameters of a Mo+5 (d1) configuration. Ultimately, I want to embed this in a small SiC cluster to investigate point-defects in this material, but as a first step I am using point charges around the central atom in the symmetry that I am interested in. In order to enforce tetrahedral symmetry and preserve the degeneracies I am using an MCSCF calculation with SUPSYM on. However, in the calculation of the g-parameter it seems like the program does not go forward because one of the degenerate orbitals is fully occupied, whereas the second is not. Occupation analysis however does show two orbitals with occupancy 0.5. Both input and output files are attached. Thank you very much in advance for your help,
Carmem Maia
Attachments
MoPointChargeTetG.out
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MoPointChargeTetG.inp
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taylor
Posts: 525
Joined: 15 Oct 2013, 05:37
First name(s): Peter
Middle name(s): Robert
Last name(s): Taylor
Affiliation: Tianjin University
Country: China

Re: Problems obtaining g-tensor in MCSCF calculation

Post by taylor » 02 Apr 2018, 12:58

First, if you would like to have exact tetrahedral symmetry, a better specification is to use D2 symmetry. In this case you would specify
Generators=2 XY XZ
to impose two-fold rotational symmetry around (respectively) the z and the y axis. Two-fold rotation around the x axis is then generated automatically from the product of these two generators (do not try to specify all three axes in input!)
Then you only need one point charge specified explicitly because the other three will be created for you, and as long as you specify that one charge as being at
a.aaaa a.aaaa a.aaaa
that is, that it has identical x, y, and z coordinates to whatever precision you input, your system will have Td symmetry.

Now, I do not say this will solve your problem. Because although you say
"...the program does not go forward because one of the degenerate orbitals is fully occupied, whereas the second is not. Occupation analysis however does show two orbitals with occupancy 0.5"
I am not at all sure this means what you might think/hope. The natural orbital occupation numbers printed at convergence do not have this property. The population analysis does, but this may be a consequence of performing the analysis in supersymmetry. I am pretty confident when the response calculation starts it is using the occupation from the NOs, and this is then broken (higher) symmetry because those occupation numbers are 1 and 0, not 0.5 and 0.5.

One way of treating these sorts of degenerate symmetries is to average over several roots of the MCSCF problem, but Dalton does not have this facility (Incidentally, you are running a quite old version of the program, you will find it difficult to get support/advice long term with an old version, although I do not say that using an old version is causing the problem here.)

Short of removing the supsym directives and running in D2 and looking at what you get, I am at a loss to know what you can do, I'm afraid.

Best regards
Pete

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