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dftbplus / skprogs

Basic programs for generating Slater-Koster files for the DFTB-method
GNU Lesser General Public License v3.0
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Exponents? #99

Open andrewshyichuk opened 1 day ago

andrewshyichuk commented 1 day ago

What is your suggested feature? Please describe.

I wonder where do I get exponents for atoms that are not in the examples. Their physical sense is not specified. I assume those are zetas for the STOs, as described in: https://en.wikipedia.org/wiki/Slater-type_orbital

If that is true - I guess I can use any basis I like and fit STOs to it?

Or, are those exponents for GTOs that approximate STOs? If so, can I use exponents from whichever basis I like, as long as it is good enough to resemble an STO? Would ANO-RCC work?

vanderhe commented 8 hours ago

Hi @andrewshyichuk,

we usually resort to even-tempered STOs, by generating the exponents according to a geometric series. If you have installed the sktools, you should see the script skexp in your PATH. For a given nuclear charge $Z$ it will print the requested amount of exponents for your STOs. The number of exponents should be chosen so that the one-center calculations are converged. A too large number of exponents will lead to linear dependencies and the slateratom code halting.

Best regards Tammo