Relativistic Effects and Spin
*****************************


Spin polarization
=================

By default Band calculations are spin-restricted. You can instruct
Band to perform a  spin-unrestricted via the "Unrestricted" key:

   Unrestricted Yes/No

"Unrestricted"
   Type:
      Bool

   Default value:
      No

   Description:
      Controls whether Band should perform a spin-unrestricted
      calculation. Spin-unrestricted calculations are computationally
      roughly twice as expensive as spin-restricted.

The orbitals are occupied according to the aufbau principle.

If you want to enforce a specific spin-polarization (instead of
occupying according to the aufbau principle) you can use the
"EnforcedSpinPolarization" key:

   EnforcedSpinPolarization float

"EnforcedSpinPolarization"
   Type:
      Float

   GUI name:
      Spin polarization

   Description:
      Enforce a specific spin-polarization instead of occupying
      according to the aufbau principle. The spin-polarization is the
      difference between the number of alpha and beta electron.
      Thus, a value of 1 means that there is one more alpha electron
      than beta electrons.                   The number may be
      anything, including zero, which may be of interest when
      searching for a spin-flipped pair, that may otherwise end up in
      the (more stable) parallel solution.


Relativistic Effects
====================

Relativistic effects are treated with the accurate and efficient ZORA
approach [1] [2], controlled by the "Relativity" keyword. Relativistic
effects are negligible for light atoms, but grow to dramatic changes
for heavy elements. A rule of thumb is: Relativistic effects are quite
small for elements of row 4, but very large for row 6 elements (and
later).

   Relativity
      Level [None | Scalar | Spin-Orbit]
   End

"Relativity"
   Type:
      Block

   Description:
      Options for relativistic effects.

   "Level"
      Type:
         Multiple Choice

      Default value:
         Scalar

      Options:
         [None, Scalar, Spin-Orbit]

      GUI name:
         Relativity (ZORA)

      Description:
         None: No relativistic effects.                      Scalar:
         Scalar relativistic ZORA.                      This option
         comes at very little cost.                      SpinOrbit:
         Spin-orbit coupled ZORA.                      This is the
         best level of theory, but it is (4-8 times) more expensive
         than a normal calculation. Spin-orbit effects are generally
         quite small, unless there are very heavy atoms in your
         system, especially with p valence electrons (like Pb).
         See also the SpinOrbitMagnetization key.

See also the SpinOrbitMagnetization key.

[1] P.H.T. Philipsen, E. van Lenthe, J.G. Snijders and E.J. Baerends,
    *Relativistic calculations on the adsorption of CO on the (111)
    surfaces of Ni, Pd, and Pt within the zeroth-order regular
    approximation.*  Physical Review B 56, 13556 (1997).

[2] P.H.T. Philipsen, and E.J. Baerends,  *Relativistic calculations
    to assess the ability of the generalized gradient approximation to
    reproduce trends in cohesive properties of solids.*  Physical
    Review B 61, 1773 (2000).
