click here). Pseudopotentials a) are adjusted to orbital energies and densities of a suitable atomic reference state, while pseudopotentials b) are generated using total valence energies of a multitude of atomic states.
Library keywords in case a) are ECP1 and ECP2; ECP2 is used when more than one pseudopotential is available for a given atom and then denotes the ECP with the smaller core definition. (For Cu, e.g., ECP1 refers to an Ar-like 18-core, while ECP2 simulates a Ne-like 10 one with the and electrons promoted to the valence shell). For accurate calculations including electron correlation, promotion of all core orbitals with main quantum number equal to any of the valence orbitals is recommended.
Library keywords in case b) are of the form ECP; is the number of core electrons which are replaced by the pseudopotential, denotes the reference system used for generating the pseudopotential (: states of the single-valence-electron ion; : states of the neutral atom and of ions with low charge), and stands for the theoretical level of the reference data (: Hartree-Fock, : quasi-relativistic; : relativistic). For one- or two-valence electron atoms , is a good choice, while otherwise , (or ) is recommended. (For light atoms, or for the discussion of relativistic effects, the corresponding pseudopotentials may be useful.) Additionally, spin-orbit (SO) potentials and core-polarization potentials (CPP) are available, to be used in connection with case b) ECPs, but these are not currently contained in the library, so explicit input is necessary here (cf. below).
In both cases, a) and b), the same keywords refer to the pseudopotential and the corresponding basis set, with a prefix MBS-...in case a).