Core-excited and shape resonances of uracil

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Abstract

Shape and core-excited resonances of uracil created when an electron is attached to this molecule are investigated with high level ab initio methods.

Abstract

Attachment of an electron to nucleobases leads to metastable anion states called resonances. There are two types of electronic resonances present in the nucleobases. Shape resonances occur when the electron is attached to one of the previously unoccupied π* orbitals of the base. An electron can also be attached to an electronically excited state leading to core-excited or Feshbach resonances. In this work we present both types of resonances of uracil, a nucleobase present in RNA. Both the positions and widths of the resonances have been calculated using a stabilization method coupled with high level electronic structure methods. Core-excited resonances which are accessed with electrons of energy >4.6 eV are expected to play an important role in the dissociative electron attachment of uracil. Mixing between configurations corresponding to shape and core-excited resonances is also present which complicates the theoretical treatment of this system and necessitates multiconfigurational approaches for a proper description.

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Advances in methods and algorithms in a modern quantum chemistry program package.

Yihan Shao, Laszlo Fusti Molnar, Yousung Jung … (2006)

Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces.