arXiv subjects

Achintya Kumar Dutta

Publications and source records attributed to Achintya Kumar Dutta.

40 records · Page 3Linked to original sources

arXiv2020

Electron attachment to Cytosine: The Role of Water

We present an EOM-CCSD based QM/MM study on the electron attachment process to cytosine, solvated in water. The microhydration studies cannot capture the effect of bulk water environment on the electron attachment process and one need to include large number of water molecules in the calculation to get converged results. The electron attachment in the bulk solvated cytosine happened through a doorway mechanism, where the initial electron is localized on water. The electron subsequently gets transferred to cytosine by mixing of electronic and nuclear degrees of freedom which happens at an ultrafast time scale. The bulk water environment stabilizes the cytosine bound anion by an extensive hydrogen-bonding network and enhances the electron transfer rate by manifold from that observed in the gas phase. The predicted adiabatic electron affinity and electron transfer rate obtained from our QM/MM calculations are consistent with the available experimental results.

physics.chem-ph↗

arXiv2020

A Core-Valence Separated Similarity Transformed EOM-CCSD Method for Core-excitation Spectra

We present the theory and implementation of a core-valence separated similarity transformed EOM-CCSD (STEOM-CCSD) method for K-edge core excitation spectra. The method can select an appropriate active space using CIS natural orbitals and near black box to use. The second similarity transformation Hamiltonian is diagonalized in the space of single excitation. Therefore, the final diagonalization step is free from the convergence problem arising because of the coupling of the core-excited states with the continuum of doubly excited states. Convergence trouble can appear for the preceding core-ionized states calculation in STEOM-CCSD. A core-valence separation scheme (CVS) compatible with the natural orbital based active space selection has been implemented to overcome the problem. The CVS-STEOM-CCSD has similar accuracy as that of the standard CVS-EOM-CCSD method but comes with a lower computational cost. The modification required for the CVS scheme because of the use of CIS natural orbital is highlighted. The suitability of CVS-STEOM-CCSD for chemical application is demonstrated by simulating the K-edge spectra of glycine and thymine.

physics.chem-ph↗

arXiv2020

Water mediated Electron Attachment to Nucleobases: Surface-bound vs Bulk Solvated Electrons

We have investigated the electron attachment dynamics of uracil in water using accurate wave-function and QM/MM methods. The initial electron attached state is found to be localized on the water and mixing of electronic and nuclear degrees of freedom leads to the transfer of electron from the water to the uracil. The water molecules around the uracil stabilize the uracil bound anion by creating an extensive hydrogen-bonding network. The presence of the bulk water environment accelerates the rate of electron attachment to uracil and the complete electron transfer from water to the uracil happens at a picosecond time scale. The degree of solvation of the aqueous electron can lead to a difference in the initial stabilization of the uracil bound anion but at a longer time scale the anion formed due to the attachment of both surface-bound and bulk solvated electrons behaves similarly.

physics.chem-ph↗

arXiv2017

Assessment of Low Scaling Approximations to EOM-CCSD Method for Ionization Potential

In this paper, we investigate the performance of different approximate variants of the EOM-CCSD method for calculation of ionization potential, as compared to EOM-CCSDT reference values. The errors in the various approximate variants of the EOM-CCSD method are quite different for different kind of ionized states. None of the approximate variants including the original EOM-CCSD method gives a uniform performance over outer valence, inner valence, and core ionization, favoring one or other, depending upon nature of the approximation used.

physics.chem-ph↗