The TDDFT equations provide an affordable yet still reasonably accurate method to calculate the electronic resonances of chemical systems. However the iterative solution of the eigenvalue problem is challenging to converge with standard methods such as the Davidson algorithm for some systems and regions of the spectrum. This is especially common in X-ray absorption spectroscopy (XAS), where there are regions with a high density of states in the interior of the spectrum. Modern solvers for non-Hermitian eigenvalue problems such as the generalized preconditioned locally harmonic residual (GPLHR) can alleviate this, but at the expense of increased computational cost. A hybrid method utilizing both methods is able to adapt to the problem to provide better computational performance while still retaining robustness of convergence.

Solving challenging TDDFT problems with a well-tempered adaptive method

256th National Meeting (2018)

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