`gexpec,rel`

at the beginning of the input. The relativistic contributions are stored by the program
within the variable `erel`. An example is

***,Cu ground state ! Pauli Hamiltonian gexpec,rel !compute relativistic correction using perturbation theory geometry={cu} !geometry basis=vtz !basis set hf !Hartree-Fock calculation e_rhf=energy+erel !store total relativistic energy in variable e_rhf

To use the 2nd-order Douglas-Kroll-Hess Hamiltonian, one has to specify

`dkho=2`

at the beginning of the input (note that the order can range from 2 to 99). The relativistic contributions are then included as part of the total energies. In this case the example reads

***,Cu ground state ! Douglas-Kroll-Hess Hamiltonian dkho=2 !activate 2nd-order Douglas-Kroll-Hess tretament geometry={cu} !geometry basis=vtz-dk !special DK basis set (mandatory!) hf !Hartree-Fock e_rhf=energy !Total relativistic energy

To use the eXact-2-Component (X2C) Hamiltonian, one has to specify

`dkho=101`

In this case the DK contracted basis sets can also be used, but special X2C contracted basis sets are prefered, e.g., vtz-x2c. These will be available soon.

molpro@molpro.net 2018-09-21