In electromagnetism, the Lorenz gauge, Lorentz Condition or Lorenz gauge condition is a partial gauge fixing of the electromagnetic vector potential. The condition is that ??. This does not completely fix the gauge: one can still make a gauge transformation where is a harmonic scalar function (that is, a scalar function satisfying , the equation of a massless scalar field).
The Lorenz condition is used to eliminate the redundant spin-0 component in the (1/2,1/2) representation of the Lorentz group. It is equally used for massive spin-1 fields where the concept of gauge transformations does not apply at all.
The Lorenz condition is named after Ludvig Lorenz. It is a Lorentz invariant condition, and is frequently called the "Lorentz condition" because of confusion with Hendrik Lorentz, after whom Lorentz covariance is named. Wikipedia, Lorentz Condition
See Also
Bearden on Tesla and EM Source Charge discussion
Lorenz condition
Hendrik Lorentz
Lorentz Force
Ludvig Lorenz