Full Configuration Interaction Excitations of Ethene and Butadiene: Resolution of an Ancient Question

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• 作者：Csaba Daday ; Simon Smart ; George H. Booth ; Ali Alavi ; Claudia Filippi
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2012
• 出版时间：November 13, 2012
• 年：2012
• 卷：8
• 期：11
• 页码：4441-4451
• 全文大小：311K
• 年卷期：v.8,no.11(November 13, 2012)
• ISSN：1549-9626

文摘

We employ the recently developed full configuration interaction quantum Monte Carlo (FCIQMC) method to compute the 蟺 鈫?蟺* vertical excitation energies of ethene and all-trans butadiene. These excitations have been the subject of extensive theoretical studies, and their location with respect to the corresponding absorption band maximum is the source of a long lingering debate. Here, we reliably estimate the vertical excitations of ethene and butadiene by performing FCIQMC calculations for spaces as large as 10¹⁸ and 10²⁹ Slater determinants, respectively. For ethene, we obtain a vertical excitation energy in the range 7.89鈥?.96 eV, depending on the particular equilibrium ground-state geometry employed, and definitely higher than the absorption maximum located at 7.66 eV. For the computationally more challenging case of butadiene, our calculations provide a robust estimate of about 6.3 eV for this excitation, that is, 0.4 eV higher than the corresponding absorption band maximum. Our FCIQMC excitation energies represent a reliable benchmarking reference for future calculations.