TY - JOUR

T1 - The charge transfer problem in density functional theory calculations of aqueously solvated molecules

AU - Isborn, Christine M.

AU - Mar, Brendan D.

AU - Curchod, Basile F E

AU - Tavernelli, Ivano

AU - Martínez, Todd J.

PY - 2013/10/10

Y1 - 2013/10/10

N2 - Recent advances in algorithms and computational hardware have enabled the calculation of excited states with time-dependent density functional theory (TDDFT) for large systems of O(1000) atoms. Unfortunately, the aqueous charge transfer problem in TDDFT (whereby many spuriously low-lying charge transfer excited states are predicted) seems to become more severe as the system size is increased. In this work, we concentrate on the common case where a chromophore is embedded in aqueous solvent. We examine the role of exchange-correlation functionals, basis set effects, ground state geometries, and the treatment of the external environment in order to assess the root cause of this problem. We conclude that the problem rests largely on water molecules at the boundary of a finite cluster model, i.e., "edge waters." We also demonstrate how the TDDFT problem can be related directly to ground state problems. These findings demand caution in the commonly employed strategy that rests on "snapshot" cutout geometries taken from ground state dynamics with molecular mechanics. We also find that the problem is largely ameliorated when the range-separated hybrid functional LC-ωPBEh is used.

AB - Recent advances in algorithms and computational hardware have enabled the calculation of excited states with time-dependent density functional theory (TDDFT) for large systems of O(1000) atoms. Unfortunately, the aqueous charge transfer problem in TDDFT (whereby many spuriously low-lying charge transfer excited states are predicted) seems to become more severe as the system size is increased. In this work, we concentrate on the common case where a chromophore is embedded in aqueous solvent. We examine the role of exchange-correlation functionals, basis set effects, ground state geometries, and the treatment of the external environment in order to assess the root cause of this problem. We conclude that the problem rests largely on water molecules at the boundary of a finite cluster model, i.e., "edge waters." We also demonstrate how the TDDFT problem can be related directly to ground state problems. These findings demand caution in the commonly employed strategy that rests on "snapshot" cutout geometries taken from ground state dynamics with molecular mechanics. We also find that the problem is largely ameliorated when the range-separated hybrid functional LC-ωPBEh is used.

UR - http://www.scopus.com/inward/record.url?scp=84885655335&partnerID=8YFLogxK

U2 - 10.1021/jp4058274

DO - 10.1021/jp4058274

M3 - Article (Academic Journal)

C2 - 23964865

AN - SCOPUS:84885655335

VL - 117

SP - 12189

EP - 12201

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 40

ER -