Quantum Monte Carlo Treatment of the Charge Transfer and Diradical Electronic Character in a Retinal Chromophore Minimal Model
Year: 2015
Type: article
Abstract: The penta-2,4-dieniminium cation (PSB3) displays similar ground state and first excited state potential energy features as those of the retinal protonated Schiff base (RPSB) chromophore in rhodopsin. Recently, PSB3 has been used to benchmark several electronic structure methods, including highly correlated multireference wave function approaches, highlighting the necessity to accurately describe the electronic correlation in order to obtain reliable properties even along the ground state (thermal) isomerization paths. In this work, we apply two quantum Monte Carlo approaches, the variational Monte Carlo and the lattice regularized diffusion Monte Carlo, to study the energetics and electronic properties of PSB3 along representative minimum energy paths and scans related to its thermal cis–trans isomerization. Quantum Monte Carlo is used in combination with the Jastrow antisymmetrized geminal power ansatz, which guarantees an accurate and balanced description of the static electronic correlation thanks to the multiconfigurational nature of the antisymmetrized geminal power term, and of the dynamical correlation, due to the presence of the Jastrow factor explicitly depending on electron–electron distances. Along the two ground state isomerization minimum energy paths of PSB3, CASSCF calculations yield wave functions having either charge transfer or diradical character in proximity of the two transition state configurations. Here, we observe that at the quantum Monte Carlo level of theory, only the transition state with charge transfer character can be located. The conical intersection, which becomes highly sloped, is observed only if the path connecting the two original CASSCF transition states is extended beyond the diradical one, namely by increasing the bond-length-alternation (BLA). These findings are in good agreement with the results obtained by MRCISD+Q calculations, and they demonstrate the importance of having an accurate description of the static and dynamical correlation when studying isomerization and transition states of conjugated systems.
DOI: 10.1021/ct501122z
Institutions: London Centre for Nanotechnology, University College London, Sapienza University of Rome, Centre National de la Recherche Scientifique, University of L'Aquila, Sorbonne Université, Laboratoire de Chimie Théorique, Université Pierre-et-Marie-Curie, Bowling Green State University, University of Siena
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,500
Funders: National Science Foundation, European Commission, Human Frontier Science Program, Partnership for Advanced Computing in Europe AISBL, Università degli Studi dell'Aquila, Directorate-General for Research and Innovation, European Research Council, Division of Chemistry, FP7 Ideas: European Research Council
Awards: Electronic Structure of Chemical, Biochemical, and Biophysical Systems: Multiscale Approach with Electron Correlation, G1552147685, G2325242462, G3528068658, G397872679, Deciphering light induced double bond isomerization in proteins, G6539456565, First principles study of photoinduced non-adiabatic dynamics in DNA repair by photolyases
OpenAlex ID: W2038264349