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Dear VASP Developers and Users,

I hope this email finds you well.

I am seeking guidance on how to calculate hyperfine interactions for a specific state, for example , the LUMO state, using VASP.

From my understanding of the VASP Wiki page, calculating the Fermi contact term requires the spin density (rho_s) for all electrons in the system, not for a specific one-electron state.

In this context, the only option available to me may involve adding an additional electron (via the NELECT tag).

Any insights or suggestions are highly appreciated.

Thank you for your assistance.

Best regards,

Saif

Saif Ullah
Research Assistant Professor
Wake Forest University
Winston-Salem, NC, USA

Dear Saif Ullah,

I am not sure what you are trying to do. So please could you supply me with more information about what you exactly want to do? Can you maybe supply a paper where something similar was already done?

All the best Jonathan

Dear Jonathan,

Thanks for your reply. In principle, Fermi Contact interaction for any one-electron state can be calculated using:
𝐴= ((4𝜇_0)/3) 𝑔_𝑒 𝜇_𝐵 𝑔_𝑁 𝜇_𝑁 |Ψ(𝑟)|^2. where, 𝜇_0, 𝜇_𝐵, 𝜇_𝑁, 𝑔_𝑒, 𝑔_𝑁, and |Ψ(𝑟)|^2 are vacuum permeability, Bohr magneton, nuclear magneton, electron g-factor, nuclear g-factor and wave-function for the desired state. Given that the wave-function for the specific one-electron level is known, one can calculate the hyperfine splitting wrt this one-electron level (LUMO for example). However, in VASP, one seems to have to solve all electrons in the system. I guess it is implemented in VASP like this.

Kind regards,
Saif

Dear Saif Ullah,

You can compute the Fermi contact interaction by setting LHYPERFINE in the INCAR file. As described on the vasp wiki, the Fermi contact interaction is computed from the electron density obtained from the electronic optimization. Therefore, it is not possible in vasp to compute the contact interaction for a LUMO state.

All the best Jonathan