SOC-compatible basis sets for transition metals
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Hi,
I am curious if Crystal accepts something like the cc-pVDZ-DK Gaussian basis set for the calculation of SOC effects in transition metals? From what I gather, it is an all electron basis set (https://www.basissetexchange.org/basis/cc-pvdz-dk/format/crystal/?version=0&elements=28). Would this require the keyword INPSOC in the basis set block of the input file?
Chris
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Hi Chris,
For SOC calculations in CRYSTAL, you cannot use all-electron basis sets directly (such as your cc-pVDZ-DK). SOC in CRYSTAL is implemented through the use of relativistic effective core potentials (ECPs), which already incorporate scalar-relativistic and spin-orbit effects for the core electrons. Thus, at least one pseudopotential is required in your system (usually on transition metals and heavier elements).
The INPSOC keyword can be used to manually insert an ECP, but the associated basis set must be designed to describe only the valence electrons that remain after introducing the pseudopotential.
I recommend checking the CRYSTAL basis set library, where you’ll find pseudopotentials and corresponding valence basis sets that are already formatted for SOC calculations in CRYSTAL. These can be used directly without modification and will ensure consistency between the basis and the relativistic treatment. However, we don't have a SOC basis set for evry element.
In the case you are interested in a specific element for wich we don't have the SOC basis, you can try using one of the internal ECP options (see page 88-92 of the manual) and combine it with a molecular basi set.
For example, you can find the basis set for the Stuttgart ECPs (STUTSC and STUTLC keyword in CRYSTAL) here. Or here for the COLUSC and COLULC ECPs. -
Hi Giacomo,
Thanks for your quick reply!
I see. So for the elements I'm interested in (Nickel and Cobalt) the "pob-DZVP" and "pob-TZVP" should be all I need for an SOC calculation, right? Since they are double- and triple-zeta valence + polarization enabled.
Chris
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Hi Chris,
Not quite, the pob-DZVP and pob-TZVP basis sets are all-electron valence basis sets, thus they are not paired with relativistic pseudopotentials. This means they cannot be used directly for spin–orbit coupling calculations in CRYSTAL.
For Nickel and Cobalt I suggest you to use the
COLUSCECP paired with the basis set that you can find here for Ni (the one under "Nickel Relativistic Effective Potential and Basis set including the 3s and 3p subshells...") and here for Co (the one under "Cobalt Relativistic Effective Potential and Basis set including the 3s and 3p subshells...").You just need to convert the valence basis set in the CRYSTAL format.
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Hi Giacomo,
Gotcha! Thanks for the thorough explanation. Using the Chromium example from the website (https://tutorials.crystalsolutions.eu/tutorials/soc/Cr3_so_colu_fmix.d12) I think it is straightforward to do the conversion to CRYSTAL.
One final question, if I may. Should I add:
TWOCOMPON
SOC
ENDtwoat the beginning or at the end of the SCF block, or it does not matter?
Chris
