MOLPRO

12 EFFECTIVE CORE POTENTIALS 79
12 EFFECTIVE CORE POTENTIALS
Pseudopotentials (effective core potentials, ECPs) may be defined at the beginning of BASIS
blocks.
The general form of the input cards is
ECP,atom,[ECP specification]
which defines a pseudopotential for an atom specified either by a chemical symbol or a group
number. The ECP specification may consist either of a single keyword, which references a
pseudopotential stored in the library, or else of an explicit definition (extending over several
input cards), cf. below.
12.1 Input from ECP library
The basis set library presently contains the pseudopotentials and associated valence basis sets
by a) the Los Alamos group (P. J. Hay and W. R. Wadt, J. Chem. Phys. 82, 270 (1985) and
following two papers), and b) the Stuttgart/Köln group (e.g., A. Nicklass, M. Dolg, H. Stoll and
H. Preuß, J. Chem. Phys. 102, 8942 (1995); for more details and proper references, see the web
page http://www.theochem.uni-stuttgart.de/pseudopotentials/). 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 18e − -core, while ECP2 simulates a Ne-like 10e − one
with the 3s and 3p 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 ECPnXY ; n is the number of core electrons which
are replaced by the pseudopotential, X denotes the reference system used for generating the
pseudopotential (X = S: single-valence-electron ion; X = M: neutral atom), and Y stands for
the theoretical level of the reference data (Y = HF: Hartree-Fock, Y = WB: quasi-relativistic;
Y = DF: relativistic). For one- or two-valence electron atoms X = S, Y = DF is a good choice,
while otherwise X = M, Y = WB (or Y = DF) is recommended. (For light atoms, or for the
discussion of relativistic effects, the corresponding Y = HF 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).
12.2 Explicit input for ECPs
For each of the pseudopotentials the following information has to be provided:
• a card of the form
ECP,atom,n core ,l max ,l ′ max;
where n core is the number of core electrons replaced by the pseudopotential V ps , l max