BEXT

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BEXT = [real array] 

Default: BEXT = 0.0 if ISPIN=2
= 3*0.0 if LNONCOLLINEAR=.TRUE.
= N/A else

Description: BEXT specifies an external magnetic field.


By means of the BEXT one may specify an external magnetic field that acts on the electrons in a Zeeman-like manner. This interaction is carried by an additional potential of the following form:

and = BEXT (in eV).
where = BEXT (in eV), and is the vector of Pauli matrices.

Heuristically, the effect of the above is most easily understood for the collinear spinpolarized case (ISPIN=2):

  • The eigenenergies of spin-up states are raised by eV, whereas the eigenenergies of spin-down states are lowered by the same amount.
  • The total energy changes by:
eV
where and are the number of up- and down-spin electrons in the system.
  • Shifting the eigenenergies of the spin-up and spin-down states w.r.t. each other may lead to a redistribution of the electrons over these states (changes in the occupancies) and hence to changes in the density with all subsequent consequences.

The energy difference between two Zeeman-splitted electronic states is given by:

where is the Bohr magneton and is the electron g-factor.

For ISPIN=2, for purely Zeeman splitted states, we have:

This leads to the following relationship between our definition of (in eV) and the magnetic field (in T):

where = 5.788 381 8060 x 10-5 eV T-1, and = 2.002 319 304 362 56.

Related tags and articles

ISPIN, LNONCOLLINEAR