The development of variational density
functional theory approaches
to excited electronic states is impeded by limitations of the commonly
used self-consistent field (SCF) procedure. A method based on a direct
optimization approach as well as the maximum overlap method is presented,
and the performance is compared with previously proposed SCF strategies.
Excited-state solutions correspond to saddle points of the energy
as a function of the electronic degrees of freedom. The approach presented
here makes use of a preconditioner determined with the help of the
maximum overlap method to guide the convergence on a target nth-order saddle point. This method is found to be more
robust and converge faster than previously proposed SCF approaches
for a set of 89 excited states of molecules. A limited-memory formulation
of the symmetric rank-one method for updating the inverse Hessian
is found to give the best performance. A conical intersection for
the carbon monoxide molecule is calculated without resorting to fractional
occupation numbers. Calculations on the excited states of the hydrogen
atom and a doubly excited state of the dihydrogen molecule using a
self-interaction corrected functional are presented. For these systems,
the self-interaction correction is found to improve the accuracy of
density functional calculations of excited states.
Recent
ultrafast experiments have unveiled the time scales of vibrational
cooling and decoherence upon photoexcitation of the diplatinum complex
[Pt2(P2O5H2)4]4– in solvents. Here, we contribute to the understanding
of the structure and dynamics of the lowest lying singlet excited
state of the model photocatalyst by performing potential energy surface
calculations and Born–Oppenheimer molecular dynamics simulations
in the gas phase and in water. Solvent effects were treated using
a multiscale quantum mechanics/molecular mechanics approach. Fast
sampling was achieved with a modified version of delta self-consistent
field implemented in the grid-based projector-augmented wave density
functional theory code. The known structural parameters and the PESs
of the first singlet and triplet excited states are correctly reproduced.
Besides, the simulations deliver clear evidence that pseudorotation
of the ligands in the excited state leads to symmetry lowering of
the Pt2P8 core. Coherence decay of Pt–Pt
stretching vibrations in solution was found to be governed by vibrational
cooling, which is in agreement with previous ultrafast experiments.
We also show that the flow of excess Pt–Pt vibrational energy
is first directed toward vibrational modes involving the ligands,
with the solvent favoring intramolecular vibrational energy redistribution.
The results are supported by thorough vibrational analysis in terms
of generalized normal modes.
A direct optimization method for obtaining excited electronic states using density functionals is presented. It involves selective convergence on saddle points on the energy surface representing the variation of the...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.