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# Effective Core Potentials

Effective-core potentials (ECP) are invoked via the keyword

ECP=ON

In addition, the use of ECPs requires that the keyword BASIS is set to SPECIAL and after that the basis-set keyword is need to be defined (as in GENBAS file) for each atom. Then (separated by a blank line), the keyword (as in ECPDATA file) to be used for ECPs need to be specified.

As an example, we show here an input for NiF6

  NiF6 single-point energy calculation using an ECP for Ni
NI
F 1 R
F 1 R 2 A
F 1 R 3 A 2 T1
F 1 R 4 A 3 T2
F 1 R 5 A 4 T1
F 1 R 6 A 5 T2

R=1.676125
A=90.
T1=90.
T2=270.

*CFOUR(CALC=HF,BASIS=SPECIAL,ECP=ON)

NI:ECP-10-MDF
F:DZP
F:DZP
F:DZP
F:DZP
F:DZP
F:DZP

NI:ECP-10-MDF
F:NONE
F:NONE
F:NONE
F:NONE
F:NONE
F:NONE


The calculation uses the .... ecp for Ni together with the corresponding basis set, while no ECP is specified for F (input NONE) and the corresponding basis set is DZP.

The ECPs must be provided in a similar manner as the basis-set via the ECPDATA file.

input and output example for a HF-SCF calculation with ECPs

Examples