# Electric and Magnetic Fields¶

## Electric Field¶

EField
Ez float
unit [Volt/Angstrom | a.u. | Volt/Bohr | Volt/meter]
End

EField
Type: Block Include a homogeneous, static, electric field in the z-direction (only possible for 0D, 1D or 2D periodic systems)
Ez
Type: Float 0.0 Strength of the electric field, in units as selected with the EField unit key.
unit
Type: Multiple Choice Volt/Angstrom [Volt/Angstrom, a.u., Volt/Bohr, Volt/meter] Unit of the electric field Ez

The static field is explicitly handled in the determination of the orbital coefficients, energy, and gradients. If you apply it to any other property, such as the NMR shielding tensor, dielectric function, solvation energy, etc., the result is probably not entirely correct (that is, it might not include the effect of the external filed). In case of doubt contact the SCM staff.

The effect of a magnetic filed can be approximated by the following potential: $$\mu_B \vec{\sigma}_i \vec{B}$$, where $$\mu_B$$ is the Bohr magneton, $$\vec{\sigma}_i$$ are the Pauli matrices and $$\vec{B}$$ is the magnetic field. For Spin-unrestricted collinear calculations, the spin is assumed to be aligned with the z-axis.

## Magnetic Field¶

BField
Bx float
By float
Bz float
Dipole [True | False]
DipoleAtom integer
Method [NR_SDOTB | NR_LDOTB | NR_SDOTB_LDOTB]
Unit [tesla | a.u.]
End

BField
Type: Block The effect of a magnetic filed can be approximated by the following potential: mu * sigma_i * B, where mu is the Bohr magneton, sigma_i are the Pauli matrices and B is the magnetic field
Bx
Type: Float 0.0 Tesla Value of the x component of the BField
By
Type: Float 0.0 Tesla Value of the y component of the BField
Bz
Type: Float 0.0 Tesla Value of the z component of the BField
Dipole
Type: Bool False Use an atomic dipole as magnetic field instead of a uniform magnetic field.
DipoleAtom
Type: Integer 1 Atom on which the magnetic dipole should be centered (if using the dipole option)
Method
Type: Multiple Choice NR_SDOTB [NR_SDOTB, NR_LDOTB, NR_SDOTB_LDOTB] There are two terms coupling to an external magnetic field. One is the intrinsic spin of the electron, called S-dot-B, the other one is the orbital momentum call L-dot-B. The L.B is implemented non-relativistically, using GIAOs in the case of a homogeneous magnetic field (not for the dipole case).
Unit
Type: Multiple Choice tesla [tesla, a.u.] Unit of magnetic filed. The a.u. is the SI version of a.u.

## Atoim-wise fuzzy potential¶

FuzzyPotential # Non-standard block. See details.
...
End

FuzzyPotential
Type: Non-standard block Atomic (fuzzy cell) based, external, electric potential. See example.

Example:

FuzzyPotential
scale \$scale
a1 v1   ! atom with index a1 gets potential coefficient v1 (a.u.)
a2 v2   ! atom a2 gets potential v2
...
End

scale

Overall scaling factor to be applied.

If an atom is not in the list it gets a coefficient of zero. The potential of an atom is its number ($$v_i$$) as specified on input times its fuzzy cell

$V(r) = \sum_i^\text{atoms} v_i \mathcal{P}_{i,U} (r)$

using the same partition function $$\mathcal{P}$$ as for the BeckeGrid. A partition function (or fuzzy cell) of an atom is close to one in the neighborhood of this atom.

The sign convention is: negative is favorable for electrons. (Unit: a.u.)