# Example: ESR g-tensor, A-tensor, self consistent spin-orbit coupling: VO¶

Download VO_collinear.run

The ESR parameters of VO are calculated with the collinear approximation for unrestricted Spin-Orbit coupled calculations. In this example the VO-molecule has three unpaired electrons.

You calculate Electron Spin Resonance properties with the keywords ESR and QTENS. ESR is a block-type key and is used to compute the G-tensor or the Nuclear Magnetic Dipole Hyperfine interaction. QTENS is a simple key and invokes the computation of the Nuclear Electric Quadrupole Hyperfine interaction.

Proper usage of the key ESR requires that you do one of the following:

1. A Spin-Orbit calculation, spin-restricted, with exactly one unpaired electron, or (b) A Spin-Orbit calculation, spin-unrestricted in the collinear approximation, or (c) No Spin-Orbit terms and spin-unrestricted.

In case (a) and (b) you obtain the G-tensor. In case (b) and (c) you get the Magnetic Dipole Hyperfine interaction.

Note: in case (a) the program also prints a Magnetic Dipole Hyperfine interaction data, but these have then been computed without the terms from the spin-density at the nucleus. Note: in case (b) and (c) one can have more than one unpaired electron. Note: in case (b) one has to use symmetry NOSYM.

Two calculations are performed:

• Scalar relativistic spin-unrestricted (case c)
• Spin-Orbit relativistic spin-unrestricted collinear (case b)

After the preliminary calculations (DIRAC, to get the relativistic TAPE12 file with relativistic potentials, and the Create runs), we first calculate the Dipole Hyperfine interaction: a spin-unrestricted calculation without Spin-Orbit coupling.

Note that one has to use ALLPOINTS in the calculation for a linear molecule to get results for the nuclear magnetic dipole hyperfine interaction. For an accurate calculation of the hyperfine interaction the numerical quality is set to VeryGood.

$ADFBIN/adf << eor Atoms V 0 0 0 O 0 0 1.589 End XC GGA Becke Perdew End esr end qtens allpoints unrestricted charge 0 3 Relativistic Scalar ZORA CorePotentials t12.rel & V 1 O 2 End NumericalQuality verygood Fragments V t21.V O t21.O End End input eor  Then a spin-orbit coupled spin-unrestricted calculation is performed using the collinear approximation. Note that symmetry NOSYM is used. $ADFBIN/adf << eor
Atoms
V 0 0 0
O 0 0 1.589
End

XC
GGA Becke Perdew
End

esr
end
qtens

symmetry nosym
unrestricted
collinear

Relativistic  Spinorbit ZORA
CorePotentials t12.rel  &
V 1
O 2
End

NumericalQuality verygood

Fragments
V t21.V
O t21.O
End
End input
eor