This keyword specifies the weight function for the grid partitioning.
SCREENED / BECKE
A screened weight function is used. This is the default.
The original Becke weight function is used. This option
also activates the calculation of weight derivatives.
The BECKE weight function  introduces a cubic scaling into the
grid generation . By introducing a new piece-wise defined weight
function , near linear scaling for the grid generation can be
obtained. This weight function is specified with the option SCREENED.