PNNL

Abstract

Accurate description of the ionization process in DNA is crucial to the understanding of the DNA damage under exposure to ionizing radiation, as well as to the exploration of the potential application of DNA strands in nano-electronics. During the last years, relevant studies have been focused on the lowest ($i.e.$ the first) valence ionization energies (VIE) of DNA bases-related species, while a clear picture of a broader ionization spectrum of longer sequence is still missing. Theoretically, this requires applying highly accurate and predictable methods on a relatively large system size ($e.g.$ several base pairs), of which the computational complexity prohibits most of the practices. In this work, by employing our recently developed Green's function coupled-cluster (GFCC) library on supercomputing facilities, we have studied the spectral functions of several guanine$-$cytosine (G$-$C) base pair structures ([G$-$C]$_n$, $n=1-3$) in a relatively broad near-valence regime ($-25\sim-5$ eV) in the coupled-cluster with singles and doubles (CCSD) level. Our focus is to give a many-body understanding of the spectral profile and feature change as the system size expands in this regime. The results show that, for the considered G$-$C base pairs, even though the lowest VIE keeps reducing as the system size expands, the spectral function profiles of all three G$-$C base pairs are very much alike in the considered regime, and the relative peak positions didn't vary by more than 0.2 eV. Further analysis of the second ionized state for each G$-$C base pair shows the total 2$h$$-$1$p$ components could contribute up to $\sim$9\% of the corresponding ionized state as more G$-$C base pairs being stacked, of which the leading 2$h$$-$1$p$ components feature a transition from the intra-base-pair cytosine $\pi\rightarrow\pi^\ast$ excitation in single layer [G$-$C]$_1$ to the inter-base-pair electron excitation in multi-layer [G$-$C]$_2$ and [G$-$C]$_3$.