Green's Function Coupled Cluster Simulation of the Near-valence Ionizations of DNA-fragments

TL;DR

This study employs Green's function coupled-cluster methods to analyze near-valence ionizations in DNA fragments, revealing size-dependent spectral features and ionization characteristics crucial for understanding DNA damage and electronic properties.

Contribution

First application of GFCC to study spectral functions of G-C base pairs in a broad near-valence regime, providing insights into size effects and ionization features in DNA fragments.

Findings

Spectral profiles and peak positions change minimally with size expansion.

Lowest vertical ionization energies decrease as system size increases.

Ionized states show significant |2h,1p⟩ character and transition from intra- to inter-base-pair excitations.

Abstract

Accurate description of the ionization process in DNA is crucial to the understanding of the DNA damage under exposure to ionizing radiation, and the exploration of the potential application of DNA strands in nano-electronics. 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]$_n$, $n=1-3$) for the first time in a relatively broad near-valence regime ([-25.0,-5.0] eV) in the coupled-cluster with singles and doubles (CCSD) level. Our focus is to give a preliminary many-body coupled-cluster understanding and guideline of the vertical ionization energy (VIE), spectral profile, and ionization feature changes of these systems as the system size expands in this near-valence regime. The results show that, as the system size expands, even though the lowest VIEs keep decreasing, the changes of spectral function profile and the relative peak positions get unexpectedly smaller. Further analysis of the ionized states associated with the most intensive peak in the spectral functions reveals non-negligible $|2h,1p\rangle$'s in the ionized wave functions of the considered G$-$C base pair systems. The leading $|2h,1p\rangle$'s associated with the main ionizations from the cytosine part of the G$-$C base pairs feature a transition from the intra-base-pair cytosine $\pi\rightarrow\pi^\ast$ excitation to the inter-base-pair electron excitation as the size of G$-$C base pairs expands, which also indicates the minimum quantum region in the many-body calculations of DNA systems.