Band is able to calculate electron paramagnetic resonance parameters of paramagnetic defects in solids: hyperfine A-tensor and the Zeeman g-tensor.
The implementation of EPR parameters in BAND are described in the publications by Kadantsev and coworkers [20] and [21]
The A-tensor is implemented within the nonrelativistic and scalar relativistic spin-polarized Kohn-Sham scheme. The A-tensor calculation is invoked by block
ATENSOR
END
Also, note that "Unrestricted" keyword should be present.
Two methods are used for A-tensor calculation.
Method 1 involves gradient of spin-polarization density and integration by parts. The isotropic component of A-tensor is obtained through integration, in a "nonlocal fashion".
In Method 2, the A-tensor is computed from spin-polarization density. Method 2 does not relies on the integration by parts. The isotropic component is obtained in a "local fashion" from the value of spin-polarization density on the grid points near the nuclei.
The user should be aware that numerical integration in A- and g-tensor routines is carried out over Wigner-Seitz (WS) cell, and, therefore, to obtain a meaningful result, the defect in question should lie at or, very close to, WS cell origin. This might require, on the user's part, some modification of the input geometry.
It also might happen that the size of the WS cell is not large enough for the adequate description of the paramagnetic defect in question. In this case, Method 1, which relies on the integration by parts and assumes that the spin-polarization density is localized inside the WS cell will fail. For the same reason, We recommend that the user removes diffuse basis set functions that describe the defect subsystem.
Finally, we note that the final result for A-tensor as presented by BAND is not scaled by the nuclear spin (as it is done in ADF) and the user is responsible for making neccessary adjustments.
The calculation of Zeeman g-tensor is invoked with block
ESR
END
The Zeeman g-tensor is implemented using two-component approach of Van Lenthe and co-workers in which the g-tensor is computed from a pair of spinors related to each other by time-reversal symmetry. The keyword "Relativistic zora spin" should be present to invoke calculations with spin-orbital coupling. The user also has to specify
Kspace 1
(Gamma-point calculation). The g-tensor is then computed from the HOMO spinor at the gamma point. In the output, the user can find two-contributions to g-tensor: one that stems from K\sigma operator and a second one, that stems from orbital angular momentum. By default, GIAO and spin-Zeeman corrections are not included, from our experience these corrections are quite small.
