Accurate Parametrization of the Non-Interacting Kinetic Energy of the Thermal Uniform Gas

There is currently tremendous interest in the XC properties of a thermal uniform gas.Here we construct an extremely accurate parametrization of the non-interacting kinetic energy for use in thermal density functional studies. Older parameterizations are either relatively crude or violate a simple relation involving the chemical potential. We use machine-learning (kernel ridge regression) to interpolate between the high- and low- temperature limits.