When BFGS is present, the the Broyden-Fletcher-Goldfarb-Shanno [19,20,21,22] procedure is used for geometry optimization. This is now an almost obsolete optimizer because other more modern methods are more efficient.  For small systems, up to about 30 atoms or 100 variables the default EF method is faster, and for larger systems the L-BFGS method - see keyword LBFGS is both faster and uses a much smaller memory.


Use BFGS for testing ideas on geometry optimization or for the very rare case where the default optimizers are not wanted.