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I have run a HF calculation on naphthalene and I have checked the MOs that have been obtained. Now, I have to select my active and inactive orbitals for CASCF(10,10). As there are 34 occupied orbitals, ORCA by default would read 31, 32, 33, 34, 35, 36, 37, 38, 39 but I have inspected how they look and I should use 27, 32, 32, 33, 34, 35, 36, 37, 41 and 48.

So the changes to be done are:

30 to 27 38 to 41 39 to 48

How do you tell ORCA to read the MOs from output file and to change the default selection of the orbitals to the ones I chose? Thank you

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You can use the "rotate" keyword in the SCF block, like

%scf rotate {30,27,90} (38,41,90} {39,48,90} end end

The "90"s mean "90 degrees", since swapping two orbitals is equivalent to applying a unitary rotation of 90 degrees. The "90"s can actually be omitted, but I'm writing them out to illustrate that you can plug in different numbers to achieve other effects (e.g. use 45 to mix two orbitals in equal portions, or 180 to flip the phase of one of the orbitals).

More details on how to perform CASSCF calculations using ORCA can be found in https://orcaforum.kofo.mpg.de/app.php/dlext/?cat=4 (only visible if you have an account on the ORCA forum and have logged in), as well as in the ORCA manual.

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  • $\begingroup$ +1 for such a quick answer, and a good one as always @wzkchem5 !! $\endgroup$ Oct 26 at 8:26
  • $\begingroup$ Thank you really much! $\endgroup$
    – Paul Logan
    Oct 26 at 9:25

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