Comparison of Solvers

At this point, it would be beneficial to compare the serial performance of the four eigensolvers we have available. The table below gives the calculation time and number of times the TDDFT operator is applied to converge the lowest 20 eigenvalues of our H$_2$ test system, containing $\sim$10,000 plane-waves.

Solver	Time (s)	# of operations
ARPACK	171	756
EA19	195	848
Conjugate Gradients	291	1290
Block Davidson	114	520

This trend in the performance is as expected from Tretiak's paper [10]. The state-by-state CG solver is not without its benefits, however, as it has very modest memory usage.