Keyword UPDATE

This keyword controls the Hessian update in quasi-Newton methods during geometry optimization or transition state search.
Options:
BFGS / POWELL / BERNY / DFP / MSP / SR1 / EXACT

	BFGS		Broyden, Fletcher, Goldfarb, Shanno (BFGS) update [207,208,209,210]. This is the default for the geometry optimization.
	POWELL		Powell update [200]. This is the default for the transition state search.
	BERNY		Berny update from H.B. Schlegel [211].
	DFP		Davidon, Fletcher, Powell update [212,213].
	MSP		Murtagh-Sargent-Powell update [197].
	SR1		Symmetric rank-one update [214].
	EXACT		No update is performed, the Hessian matrix is always calculated anew.
	VIB=$<$Real$>$		Scaling factor for the numerical step size during the calculation of second derivatives. Only valid in combination with the EXACT option.

Description:
For the optimization in redundant and Cartesian coordinates, the BFGS update is recommended. For optimization in internal coordinates, the BERNY update may be preferred. For the transition state search, only the POWELL or MSP updates are suitable. The option VIB is valid only if the option EXACT is also specified. For more information on this option see the keyword FREQUENCY (4.8.1).