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37.5 Density fitting

In order to be able to study interactions between extended monomers one can use density fitting to approximate the integrals in SAPT [7]. For this one may use the input:


with in the basis section defined jkfit and mp2fit fitting basis sets (see section 15).

Currently only the ALDA xc-kernel is implemented for the case SAPT_LEVEL=3 and SAPT_FITLEVEL=3. This means that a corresponding SAPT calculation would be uncompatible with hybrid-DFT monomer orbitals/orbital energies. Therefore it is recommended to use nonhybrid functionals in the case the dispersion/exchange-dispersion energy terms are requested in a DF-DFT-SAPT run. Another possibility is to localise the xc-potential via, e.g., the OEP method (see also example in section 37.7.3). 2018-07-22