TDDFT investigation on nucleic acid bases: Comparison with experiments and standard approach

• Published in: Journal of computational chemistry Vol. 25; no. 5; pp. 768 - 778
• Main Authors: Shukla, M.K., Leszczynski, Jerzy
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 15.04.2004
• Subjects: Adenine - chemistry; Cytosine - chemistry; electronic transition; excited state; Guanine - chemistry; Models, Molecular; nucleic acid bases; Nucleic Acids - chemistry; Rydberg contamination; TD-DFT method; Thermodynamics; Thymine - chemistry; Uracil - chemistry
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.20007

A comprehensive theoretical study of electronic transitions of canonical nucleic acid bases, namely guanine, adenine, cytosine, uracil, and thymine, was performed. Ground state geometries were optimized at the MP2/6‐311G(d,p) level. The nature of respective potential energy surfaces was determined using the harmonic vibrational frequency analysis. The MP2 optimized geometries were used to compute electronic vertical singlet transition energies at the time‐dependent density functional theory (TDDFT) level using the B3LYP functional. The 6‐311++G(d,p), 6‐311(2+,2+)G(d,p), 6‐311(3+,3+)G(df,pd), and 6‐311(5+,5+)G(df,pd) basis sets were used for the transition energy calculations. Computed transition energies were found in good agreement with the corresponding experimental data. However, in higher transitions, the Rydberg contaminations were also obtained. The existence of πσ* type Rydberg transition was found near the lowest singlet ππ* state of all bases, which may be responsible for the ultrafast deactivation process in nucleic acid bases. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 768–778, 2004