Triplet tuning – A new 'black-box' computational scheme for photochemically active molecules

Lin, Zhou

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https://hdl.handle.net/2142/96803 Copy

Description

Title

Triplet tuning – A new 'black-box' computational scheme for photochemically active molecules

Author(s)

Lin, Zhou

Contributor(s)

Van Voorhis, Troy

Issue Date

2017-06-21

Keyword(s)

Theory and computation

Abstract

Density functional theory (DFT) is an efficient computational tool that plays an indispensable role in the design and screening of $pi$-conjugated organic molecules with photochemical significance. However, due to intrinsic problems in DFT such as self-interaction error, the accurate prediction of energy levels is still a challenging task.footnote{A. Dreuw and M. Head-Gordon, {it Chem. Rev.} {bf 105}, 4009 (2015).} Functionals can be parameterized to correct these problems, but the parameters that make a well-behaved functional are system-dependent rather than universal in most cases. To alleviate both problems, optimally tuned range-separated hybrid functionals were introduced, in which the range-separation parameter, $omega$, can be adjusted to impose Koopman's theorem, $varepsilon_{rm HOMO} = -I$. These functionals turned out to be good estimators for asymptotic properties like $varepsilon_{rm HOMO}$ and $varepsilon_{rm LUMO}$.footnote{O. A. Vydrov and G. E. Scuseria, {it J. Chem. Phys.} {bf 125}, 234109 (2006).}$^,$footnote{L. Kronik, T. Stein, S. Refaely-Abramson, and R. Baer, {it J. Chem. Theory Comput.} {bf 8}, 1515 (2012).} In the present study, we propose a ``black-box'' procedure that allows an automatic construction of molecule-specific range-separated hybrid functionals following the idea of such optimal tuning. However, instead of focusing on $varepsilon_{rm HOMO}$ and $varepsilon_{rm LUMO}$, we target more local, photochemistry-relevant energy levels such as the lowest triplet state, T$_1$. In practice, we minimize the difference between two $E_{{rm T}_1}$'s that are obtained from two DFT-based approaches, $Delta$-SCF and linear-response TDDFT. We achieve this minimization using a non-empirical adjustment of two parameters in the range-separated hybrid functional -- $omega$, and the percentage of Hartree--Fock contribution in the short-range exchange, $c_{rm HF}$. We apply this triplet tuning scheme to a variety of organic molecules with important photochemical applications, including laser dyes, photovoltaics, and light-emitting diodes, and achieved good agreements with the spectroscopic measurements for $E_{{rm T}_1}$'s and related local properties.footnote{Z. Lin and T. A. Van Voorhis, {it in preparation for submission to J. Chem. Theory Comput.}}

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/96803

DOI

https://doi.org/10.15278/isms.2017.WI11

Copyright and License Information

Copyright 2017 Zhou Lin

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