Keyword EXCITATION

This keyword specifies a time-dependent DFT (TDDFT) calculation.
Options:
DAVIDSON / RS / DSYEV / D&C / JACOBI

	DAVIDSON		Iterative Davidson diagonalization of the TDDFT matrix.
	RS		EISPACK Householder diagonalization of the TDDFT matrix. This is the default.
	DSYEV		LAPACK Householder diagonalization of the TDDFT matrix.
	D&C		LAPACK divide and conquer diagonalization of the TDDFT matrix.
	JACOBI		Jacobi diagonalization of the TDDFT matrix.
	TDA		Activation of Tamm-Dancoff approximation.

Description:
Excitation energies and oscillator strengths are calculated using the formulation of Ref. [12,35,248]. If full diagonalization is used, i.e., the option DAVIDSON is not used, then the oscillator strength sums are exact for the orbital basis set. In particular, this means that the dipole polarizability calculated as an oscillator strength sum is an analytic derivative value which should agree with the dipole polarizability found by the finite difference or other method. Note that if the Tamm-Dancoff approximation is used, the oscillator strength sums are no longer exact. The Tamm-Dancoff approximation [249,250] can actually improve the quality of computed excitation energies when the molecular geometry is far from the equilibrium geometry.