19.1.13 G96: Gill's 1996 Gradient Corrected Exchange Functional

P. M. W. Gill, Mol. Phys. 89, 433 (1996)

$$K= \sum_s \rho_{s}^{4/3}\left (\alpha-{\frac {1}{137}} \chi_{s}^{3/2}\right ) ,$$ (63)

where

$$\alpha=-\frac{3}{2}\left (\frac{3}{4\pi}\right )^{1/3} .$$ (64)