Revisiting the Thomas–Fermi potential for three-dimensional condensed matter systems

Abstract

We proposed a formally exact, probabilistic method to assess the validity of the Thomas–Fermi potential for three-dimensional condensed matter systems where electron dynamics is constrained to the Fermi surface. Our method, which relies on accurate solutions of the radial Schrödinger equation, yields the probability density function for momentum transfer. This allows for the computation of its expectation values, which can be compared with unity to confirm the validity of the Thomas–Fermi approximation. We applied this method to three n-type direct-gap III–V model semiconductors (GaAs, InAs, InSb) and found that the Thomas–Fermi approximation is certainly valid at high electron densities. In these cases, the probability density function exhibits the same profile, irrespective of the material under scrutiny. Furthermore, we show that this approximation can lead to serious errors in the computation of observables when applied to GaAs at zero temperature for most electron densities under scrutiny.

The Thomas-Fermi potential \(V_\textrm{ei}^\textrm{TF}\left( r\right) \) and the the exponential cosine screened Coulomb potential \(V_\textrm{ei}^\textrm{EC}\left( r\right) \) in coordinate space r, from the full interaction potential \(V_\textrm{ei}^\textrm{RPA}\left( q\right) \) in the momentum space q at Random Phase approximation, through suitable Fourier transforms