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# 8.12.2 Combining ECPs

(February 4, 2022)

If you wish, you can use different ECP sets for different elements in the system. This is especially useful if you would like to use a particular ECP but find that it is not available for all of the elements in your molecule. To combine different ECP sets, you set the ECP and BASIS keywords to “GEN” or (equivalently) “GENERAL”, and then add a $ecp block and a$basis block to your input file. In each of these blocks, you must name the ECP and the orbital basis set that you wish to use, separating each element by “****”. There is also a built-in combination that can be invoked specifying ECP = fit-LACVP. It automatically assigns 6-31G for atoms H–Ar and fit-LANL2DZ for heavier atoms.