In
quantum mechanics, and in particular
quantum chemistry, the
electronic density is a measure of the probability of an
electron occupying an infinitesimal element of space surrounding any given point. It is a scalar quantity depending upon three spatial variables and is typically denoted as either
ρ(
r) or
n(
r). The density is determined, through definition, by the normalized
N-electron
wavefunction which itself depends upon 4
N variables (3
N spatial and
N spin coordinates). Conversely, the density determines the wave function modulo a phase factor, providing the formal foundation of
density functional theory.