Isotope shift calculations

To run isotope shift calculations using the pCI code package, one simply has to add a few keys to the HFD.INP, BASS.INP and CONF.INP files, then run the CI procedure as usual. The main keys used for isotope shifts are the following:

• K_is - defines type of isotope shift to calculate

  • K_is = 0 - no isotope shift

  • K_is = 1 - field shift

  • K_is = 2 - specific mass shift

  • K_is = 3 - normal mass shift

  • K_is = 4 - total mass shift

• C_is - prefactor for IS perturbation (C_is = dR_nucl/R_nucl)

• Klow - lower component key

Note

For isotope shifts, it is important to recompile basc and conf with arrays for 2-electron integrals set to double precision type. This can be done in the params.f90 file by changing the value of Integer, Parameter :: type2_real = sp from sp to dp. You can confirm this change in the title of the BASC.RES and CONF.RES output files, which should mention double precision for 2e integrals.

via pCI-py scripts

Isotope shift calculations can also be automated using the pCI-py scripts. To do this, simply set the keys in the config.yml file. For example, we can set our field shift calculation with C_is=0.01:

optional:
    isotope_shifts:
        include: True
        K_is: 1
        C_is: 0.01