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Interface to DKH by A. Wolf, M. Reiher, and B. A. Hess

Code author: Justin M. Turney

Section author: Justin M. Turney

Module: DKH


For all electron calculations one can use the Douglas-Kroll-Hess (DKH) Hamiltonian to take into account scalar relativistic effects.

Minimal input for DKH single-point computation looks like this:

molecule {

set basis aug-cc-pvdz-dk
set relativistic dkh


By default a 2nd-order DKH calculation is performed. To change the default order use the DKH_ORDER option. The version of the code found in Psi4 is capable of up to 4th-order DKH calculations.



Relativistic Hamiltonian type

  • Type: string
  • Possible Values: NO, X2C
  • Default: NO


Order of Douglas-Kroll-Hess

  • Type: integer
  • Default: 2


When using this code please make reference to the appropriate following paper:

  • “The Generalized Douglas-Kroll Transformation,” A. Wolf, M. Reiher, and B. A. Hess, J. Chem. Phys. 117, 9215 (2002). (doi: 10.1063/1.1515314)