ESR

Electron Spin Resonance properties are accessible with the keywords ESR and Qtens.

ESR is a block-type keyword that invokes calculation of the g-tensor [95] as well as the Nuclear Magnetic Dipole Hyperfine interaction (A-tensor) [96].

ESR
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ESR is a block-type key, although it has not (yet) any data records to specify options or parameters. You can use the key in three situations:

• 1. In a Spin-Orbit spin restricted relativistic calculation the program will compute the G-tensor
  (Zeeman interaction). There must be exactly one unpaired electron (Kramer's Pair).
• 2. In a Spin-Orbit spin unrestricted relativistic calculation the program will compute the G-tensor
  and the Nuclear Magnetic Dipole Hyperfine interaction (A-tensor). The calculation must
  use the collinear approximation. There may be more than one unpaired electron.
• 3. If the Spin-Orbit feature is turned off, the calculation must be spin-unrestricted and apply to an
  open-shell system. The program will compute the Nuclear Magnetic Dipole Hyperfine interaction (A-tensor).

In case (1), the program will also calculate and print the Nuclear Magnetic Dipole Hyperfine interaction, but the terms due to the spin-polarization density at the nucleus are absent. Furthermore, if there is more than one unpaired electron, the computed results will simply be incorrect, without any warning from the program.

For the computation of the A-tensor, the Nuclear Magnetic Dipole Hyperfine interaction, an accurate evaluation of the spin-polarization density at the nucleus is important. This is best achieved in an all-electron calculation, avoiding any frozen core approximation.

Somewhat different ESR/EPR functionality is available from the CLGEPR (or briefly EPR) program which is described in the 'ADF Property Programs' documentation.

QTENS

This key activates the computation of the Nuclear Electric Quadrupole Hyperfine interaction. It can be applied to open-shell and to closed-shell systems.Qtens gives you the Nuclear Electric Quadrupole Hyperfine interaction (Q-tensor) [97]. The latter is directly related to the Electric Field Gradient (EFG) . The Q-tensor elements (in MHz) equal the the electric field gradient tensor elements (in a.u.) times 234.9647 times the nuclear quadrupole moment (NQM in barn units, 1 barn = 10-28m2=10-24cm2) and divided by 2I(2I-1), where I is the nuclear spin. The Nuclear Quadrupole Coupling Constant (NQCC) (in MHz) is the largest value of the principal values of the EFG (in a.u.) times 234.9647 times the nuclear quadrupole moment (in barn units). The electric field gradient tensor is printed next to the Q-tensor.