Example: Dispersion Coefficients: HF¶
General dispersion coefficients (beyond de dipole-dipole C6 interaction coefficient) are computed with the auxiliary program DISPER. It uses two output files from previous ADF Response calculations. In the example, the two ADF runs are one and the same and the relevant TENSOR output file is used twice.
$ADFBIN/adf <<EOR title Van der Waals coefficients HF atoms H 0 0 -0.8708056087 F 0 0 0.04619439132 end Basis Type DZP Core Small End symmetry C(8v) RESPONSE MAXWAALS 8 VANDERWAALS 7 ALLTENSOR ALLCOMPONENTS END end input EOR
Polarizabilities are computed at 7 (imaginary) frequencies between 0 and infinity. The program determines internally the actual frequency values in this range to use. The user only specifies the number of them, thereby determining the precision of, in fact, a numerical integration over the zero-infinity frequency range. A value of 7 is rather low.
MaxWaals determines that not only the C6 but also C7 and C8 coefficients are computed. A value higher than 8 would not be recommended, because the available basis sets would be inadequate for higher coefficients.
In DISPER calculations the preparatory Response calculation must use the AllTensor and AllComponents subkeys.
The calculation produces a file TENSOR. The subsequent DISPER run uses two such files. In this example, both are taken from the same ADF run, copying the TENSOR file to, respectively, tensorA and tensorB. These names are prescribed for a DISPER calculation.
cp TENSOR tensorA cp TENSOR tensorB $ADFBIN/disper -n1 << eor eor
The DISPER program needs no other input than just the files tensorA and tensorB, which must both be present as local files. Note the ‘-n1’ flag: this enforces that a single-node (non-parallel) run is performed. The current implementation does not support parallelization of DISPER, because the kid processes may not have the (local to the master!) files tensorA and tensorB.