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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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223. X. Feng, E. Epifanovski, J. Gauss, and A.I. Krylov
Implementation of analytic gradients for CCSD and EOM-CCSD using Cholesky decomposition of the electron-repulsion integrals and their derivatives: Theory and benchmarks
J. Chem. Phys. , submitted (2019)  

222. P. Nijjar, A. I. Krylov, O. Prezhdo, A. Vilesov, and C. Wittig
Triplet excitons in small helium clusters
J. Phys. Chem. A , submitted (2019)  

221. A.V. Nemukhin, B.L. Grigorenko, M. Khrenova, and A.I. Krylov
Computational challenges in modeling of representative bioimaging proteins: GFP-Like proteins, flavoproteins, and phytochromes
J. Phys. Chem. B , in press (2019)  

220. A. Barrozo, B. Xu, A. O. Gunina, M. Jacobs, K. Wilson, O. Kostko, M. Ahmed, and A.I. Krylov
To be or not to be a molecular ion: The role of the solvent in photoionization of arginine
J. Phys. Chem. Lett.  10, 1860 – 1865 (2019)    

219. M. L. Vidal, X. Feng, E. Epifanovsky, A.I. Krylov, and S. Coriani
A new and efficient equation-of-motion coupled-cluster framework for core-excited and core-ionized states
J. Chem. Theo. Comp. , in press (2019)   Preprint

218. S. Gulania, T.-C. Jagau, and A.I. Krylov
EOM-CC guide to Fock-space travel: The C2 edition
Faraday Disc. , in press (2019)   Preprint

217. B. L. Grigorenko, E. D. Kots, A. I. Krylov, and A. V. Nemukhin
Modeling of the glycine tripeptide cyclization in the Ser65Gly/Tyr66Gly mutant of green fluorescent protein
Mendeleev Comm.  29, 187 – 189 (2019)     

216. P. Pokhilko, R. Shannon, D. Glowacki, H. Wang, and A.I. Krylov
Spin-forbidden channels in reactions of unsaturated hydrocarbons with O(3P)
J. Phys. Chem. A  123, 482 – 491 (2019)     Preprint

215. K.D. Nanda, A.I. Krylov, and J. Gauss
Communication: The pole structure of the dynamical polarizability tensor in equation-of-motion coupled-cluster theory
J. Chem. Phys.  149, 141101 (2018)    

214. A.I. Krylov, T. Windus, T. Barnes, E. Marin-Rimoldi, J. Nash, B. Pritchard, D. Smith, D. Altarawy, P. Saxe, C. Clementi, T. D. Crawford, R. Harrison, S. Jha, V. Pande, and T. Head-Gordon
Computational chemistry software and its advancement: Three Grand Challenge cases for computational molecular science
J. Chem. Phys.  149, 180901 (2018)    

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