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Anna Krylov

Gabilan Distinguished Professor in Science and Engineering and Professor of Chemistry
Physical Chemistry

Ph.D., 1996, The Hebrew University of Jerusalem
M.Sc., 1990 , Moscow State University
Office: SSC 409A
Phone: (213) 740-4929
Fax: (213) 740-3972
 Group Homepage

Research Focus


Open-shell species: A challenge to electronic structure theory

Our research is focused on theoretical modeling of open-shell species. Since chemical transformations involve bond-breaking, radicals and diradicals are often encountered as reaction intermediates or transition states. Therefore, they play a central role in mechanistic understanding of processes important in the environment, synthetic chemistry, material science, biochemistry, etc. Since these open-shell species are often very reactive and short-lived, their experimental observations are difficult. That is why electronic structure theory is a valuable tool for studying their properties.

Radiation-induced or oxidative damage of DNA involves ionization of nucleic acid bases producing radical cations. Modulated by local interactions (h-bonding, pi-stacking, electrostatics), the hole migrates along the strand causing a variety of structural changes. Using EOM-IP-CCSD, we characterized the effect of non-covalent interactions on ionization energies of the bases.

We develop new theoretical tools that enable accurate and efficient description of properties of open-shell species, such as their energies, spectroscopy, and reactivity. This involves development of new ab initio methods within equation-of-motion coupled-cluster formalism, as well as creating interfaces between electronic structure theory and spectroscopy modeling for more direct comparison with experimental measurements. To study molecules in realistic environments (e.g., chromophores in solutions or in proteins) we employ Effective Fragment Potential method and hybrid QM/MM approach.

In equation-of-motion coupled-cluster approach, problematic open-shell states are described as "excitations" from a well-behaved closed-shell reference wave function. The amplitudes R are found by diagonalization of similarity-transformed Hamiltonian exp(-T)Hexp(T). Among important contributions from our group are: the Spin-Flip method, calculation of Dyson orbitals for open-shell and electronically excited states, a variety of properties calculations. Efficient C++ computer codes developed in Krylov's group are integrated in the Q-Chem electronic structure package.

By using new methodology and in collaboration with excellent experimental groups at USC and around the world, we study a variety of fascinating systems ranging from the species relative to atmospheric chemistry and combustion to such biologically important systems as green fluorescent protein chromophores and building blocks of DNA. A common theme in these studies is characterization of bonding in open-shell compounds and understanding the fundamental rules that governs their electronic structure and their interaction with light.

pi-stacking interactions reduce ionization energies of nucleobases by as much as 0.3-0.4 eV. The effect is due to hole delocalization and can be explained within simple molecular orbital framework. Above: The molecular orbitals and ionization energies of thymine and its pi-stacked dimer. Note that ionization also changes bonding from non-covalent to covalent, which induces significant structural changes.


Using a variety of quantum chemistry tools, we characterized the electronically excited and ionized states of green fluorescent protein and discovered that the bright absorbing state is embedded in photodetachment continuum. To understand the effect of environment on electronic properties, we also develop methods for including solvent in ab initio calculations.

More details can be found on Krylov's group website and iOpenShell. Some of the essential concepts of our research are explained in these shorts films: "Shine a light" and "Laser"


Selected publications


Latest 10 publications
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191. M. Khrenova, I. Polyakov, B.L. Grigorenko, A.I. Krylov, and A.V. Nemukhin
Improving the design of the triple-decker motif in red fluorescent proteins
J. Phys. Chem. B., submitted (2017)  

190. K.D. Nanda and A.I. Krylov
Visualizing the contributions of virtual states to two-photon absorption cross-sections by natural transition orbitals of response transition density matrices
J. Phys. Chem. Lett. 8, 3256 – 3265 (2017)     

189. E. Hossain, S.M. Deng, S. Gozem, A.I. Krylov, X.-B. Wang, and P.G. Wenthold
Photoelectron spectroscopy study of quinonimides
J. Am. Chem. Soc. 139, 11138 – 11148 (2017)    

188. A. Sadybekov and A.I. Krylov
Coupled-cluster based approach for core-level states in condensed phase: Theory and application to different protonated forms of aqueous glycine
J. Chem. Phys. 147, 014107 (2017)     

187. K.D. Nanda and A.I. Krylov
Effect of the diradical character on static polarizabilities and two-photon absorption cross-sections: A closer look with spin-flip equation-of-motion coupled-cluster singles and doubles method
J. Chem. Phys. 146, 224103 (2017)     

186. S. Xu, J. Smith, S. Gozem, A.I. Krylov, and J.M. Weber
Electronic spectra of tris(2,2'-bipyridine)-M(II) complex ions in vacuo (M = Fe and Os)
Inorg. Chem. 56, 7029 – 7037 (2017)    

185. B.L. Grigorenko, A.I. Krylov, and A.V. Nemukhin
Molecular modeling clarifies the mechanism of chromophore maturation in the green fluorescent protein
J. Am. Chem. Soc. 139, 10239 – 10249 (2017)    

184. M. de Wergifosse, A.L. Houk, A.I. Krylov, and C.G. Elles
Two-photon absorption spectroscopy of trans-stilbene, cis-stilbene, and phenanthrene: Theory and experiment
J. Chem. Phys. 146, 144305 (2017)    

183. M. de Wergifosse, C.G. Elles, and A.I. Krylov
Two-photon absorption spectroscopy of stilbene and phenanthrene: Excited-state analysis and comparison with ethylene and toluene
J. Chem. Phys. 146, 174102 (2017)    

182. K.Z. Ibrahim, E. Epifanovsky, S. Williams, and A.I. Krylov
Cross-scale efficient tensor contractions for coupled cluster computations through multiple programming model backends
J. Parallel Distrib. Comput. 106, 92 – 105 (2017)    

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