arXiv subjects

Ravindra Shinde

Publications and source records attributed to Ravindra Shinde.

23 records · Page 2Linked to original sources

arXiv2016

Ab initio Calculations of Optical Properties of Clusters

We have performed systematic large-scale all-electron correlated calculations on boron Bn, aluminum Aln and magnesium Mgn clusters (n=2--5), to study their linear optical absorption spectra. Several possible isomers of each cluster were considered, and their geometries were optimized at the coupled-cluster singles doubles (CCSD) level of theory. Using the optimized ground-state geometries, excited states of different clusters were computed using the multi-reference singles-doubles configuration interaction (MRSDCI) approach, which includes electron correlation effects at a sophisticated level. These CI wavefunctions were used to compute the transition dipole matrix elements connecting the ground and various excited states of different clusters, eventually leading to their linear absorption spectra. The convergence of our results with respect to the basis sets, and the size of the CI expansion was carefully examined. Isomers of a given cluster show a distinct signature spectrum, indicating a strong structure property relationship. This fact can be used in experiments to distinguish between different isomers of a cluster. Owing to the sophistication of our calculations, our results can be used for benchmarking of the absorption spectra and be used to design superior time-dependent density functional theoretical (TDDFT) approaches. The contribution of configurations to many-body wavefunction of various excited states suggests that in most cases optical excitations involved are collective, and plasmonic in nature. Optical absorption in planar boron clusters in wheel shape, B7, B8 and B9 computed using EOM-CCSD approach, have been compared to the results obtained from TDDFT approach with a number of functionals. This benchmarking reveals that range-separated functionals such as wB97xD and CAM-B3LYP give qualitatively as well as quantitatively the same results as that of EOM-CCSD.

physics.atm-clus↗

arXiv2014

Large-scale first principles configuration interaction calculations of optical absorption in aluminum clusters

We report the linear optical absorption spectra of aluminum clusters Al$_{n}$ (n=2--5) involving valence transitions, computed using the large-scale all-electron configuration interaction (CI) methodology. Several low-lying isomers of each cluster were considered, and their geometries were optimized at the coupled-cluster singles doubles (CCSD) level of theory. With these optimized ground-state geometries, excited states of different clusters were computed using the multi-reference singles-doubles configuration-interaction (MRSDCI) approach, which includes electron correlation effects at a sophisticated level. These CI wave functions were used to compute the transition dipole matrix elements connecting the ground and various excited states of different clusters, and thus their photoabsorption spectra. The convergence of our results with respect to the basis sets, and the size of the CI expansion, was carefully examined. Our results were found to be significantly different as compared to those obtained using time-dependent density functional theory (TDDFT) [Deshpande \textit{et al. Phys. Rev. B}, 2003, \textbf{68}, 035428]. When compared to available experimental data for the isomers of Al$_{2}$ and Al$_{3}$, our results are in very good agreement as far as important peak positions are concerned. The contribution of configurations to many body wavefunction of various excited states suggests that in most cases optical excitations involved are collective, and plasmonic in nature.

physics.atm-clus↗

arXiv2012

Optical Absorption in B$_{13}$ Cluster: A Time-Dependent Density Functional Approach

The linear optical absorption spectra of three isomers of planar boron cluster B$_{13}$ are calculated using time-dependent spin-polarized density functional approach. The geometries of these cluster are optimized at the B3LYP/6-311+G* level of theory. Even though the isomers are almost degenerate, the calculated spectra are quite different, indicating a strong structure-property relationship. Therefore, these computed spectra can be used in the photo-absorption experiments to distinguish between different isomers of a cluster.

physics.atm-clus↗

arXiv2012

Optical absorption in boron clusters B$_{6}$ and B$_{6}^{+}$ : A first principles configuration interaction approach

The linear optical absorption spectra in neutral boron cluster B$_{6}$ and cationic B$_{6}^{+}$ are calculated using a first principles correlated electron approach. The geometries of several low-lying isomers of these clusters were optimized at the coupled-cluster singles doubles (CCSD) level of theory. With these optimized ground-state geometries, excited states of different isomers were computed using the singles configuration-interaction (SCI) approach. The many body wavefunctions of various excited states have been analysed and the nature of optical excitation involved are found to be of collective, plasmonic type.

physics.atm-clus↗

arXiv2012

Large-scale first principles configuration interaction calculations of optical absorption in boron clusters

We have performed systematic large-scale all-electron correlated calculations on boron clusters B$_{n}$(n=2--5), to study their linear optical absorption spectra. Several possible isomers of each cluster were considered, and their geometries were optimized at the coupled-cluster singles doubles (CCSD) level of theory. Using the optimized ground-state geometries, excited states of different clusters were computed using the multi-reference singles-doubles configuration-interaction (MRSDCI) approach, which includes electron correlation effects at a sophisticated level. These CI wave functions were used to compute the transition dipole matrix elements connecting the ground and various excited states of different clusters, eventually leading to their linear absorption spectra. The convergence of our results with respect to the basis sets, and the size of the CI expansion were carefully examined. The contribution of configurations to many body wavefunction of various excited states suggests that the excitations involved are collective, plasmonic type.

physics.atm-clus↗