All-electron Configuration Interaction Research Articles

TaN, a molecular system for probingP,T-violating hadron physics

All-electron configuration interaction theory in the framework of the Dirac-Coulomb Hamiltonian has been applied to the TaN molecule, a promising candidate in the search for Beyond-Standard-Model physics in both the hadron and the lepton sector of matter. We obtain in the first excited {$^3\Delta_1$} state a ${\cal{P,T}}$-odd effective electric field of $36.0 \left[\frac{\rm GV}{\rm cm}\right]$, a scalar-pseudoscalar ${\cal{P,T}}$-odd interaction constant of $32.8$ [kHz], and a nuclear magnetic-quadrupole moment interaction constant of $0.74$ [$\frac{10^{33} {\text{Hz}}}{e\, {\text{cm}}^2}$]. The latter interaction constant has been obtained with a new approach which we describe in detail. Using the same highly correlated all-electron wavefunctions with up to $2.5$ billion expansion terms, we obtain a parallel magnetic hyperfine interaction constant of $-2954$ [MHz] for the $\rm {^{181}{T}a}$ nucleus, a very large molecule-frame electric dipole moment of $-4.91$ [Debye], and spectroscopic constants for the four lowest-lying electronic states of the molecule.

Spin–orbit all-electron configuration interaction study on the electronic structure and radiative lifetimes of low-lying excited states of CdH

We calculated the potential energy curves of 10 Λ-S states correlated with the five lowest dissociation limits of the CdH radical by a configuration interaction method, as well as those of 17 Ω states generated from the Λ-S states. The spectroscopic parameters of bound states were calculated and found to be well consistent with the latest experimental results. We also discussed the possible predissociation mechanisms of C2Σ+, 42Σ+ and 22Π states on the basis of the calculation of spin–orbit elements. Finally, the allowed transition dipole moments and the radiative lifetimes of A2Π, B2Σ+ and C2Σ+ states were obtained.

All-electron configuration interaction study on potential energy curves of low-lying excited states and spectroscopic properties of SiS

The 18 -S states correlated to the lowest dissociation (Si(3Pg)+S(3Pg)) limit are computed with high-level multireference configuration interaction (MRCI(SD)) approach through utilizing all-electron aug-cc-pwCVQZ-DK basis set. The scalar relativistic effect and the core-valence correlation effect of Si (2s22p6) and S (2s22p6) are taken into account. On the basis of calculated potential energy curves, the spectroscopic constants of the bound states are fitted, including equilibrium distance Re, adiabatic transition energies Te, harmonic vibrational frequencies e, anharmonic terms exe, and rotational constant Be. The electronic configurations at different bond lengths are given. The electronic dipole moments of 18 -S states are calculated, illuminating the influence of electronic configuration variation on electronic dipole moment. With the help of nonvanishing spin-orbit matrix elements including b3 and A1 as a function of the internuclear distance, the nearby state perturbations to b3 and A1 are discussed in detail. Finally, the transition dipole moments and Franck-Condon factors of A1X1+ and E1+X1+ transitions are obtained, and radiative lifetimes of five lowest vibrational levels of the two singlet excited states are evaluated.

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

We report the linear optical absorption spectra of aluminum clusters Aln (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 et al. Phys. Rev. B: Condens. Matter Mater. Phys., 2003, 68, 035428]. When compared to the available experimental data for the isomers of Al2 and Al3, our results are in very good agreement as far as important peak positions are concerned. The contribution of configurations to many body wave functions of various excited states suggests that in most cases optical excitations involved are collective, and plasmonic in nature.

Ab-initio CI calculations for 3d transition metal L2,3 X-ray absorption spectra of TiCl4 and VOCl3

X-ray-absorption near-edge structures (XANES) at the transition metal (TM) L2,3-edge of TiCl4 and VOCl3 are calculated by the all-electron configuration interaction (CI) method using fully-relativistic molecular spinors with density functional theory (DFT). The electronic excitation from molecular spinors mainly composed of ligand p atomic spinors to those of TM-3d spinors, i.e., the charge transfer, is included by taking additional electronic configurations in the CI. The effects of the ligand field and the charge transfer on the TM-L2,3 XANES are investigated by an ab-intio method. The reduction of inter-electron interaction due to the covalent bonding between TM and ligand atoms has been found. The contribution of charge transferred configuration is small at the initial state of TM-L2,3 XANES while the significant amount of charge transferred configuration is found at the final states. The spectral shapes of TM-L2,3 XANES of both TiCl4 and VOCl3 are strongly modified by the charge transfer effects.

All-electron CI calculations of 3d transition-metalL2,3 XANES using zeroth-order regular approximation for relativistic effects

X-ray-absorption near-edge structures (XANES) at 3d transition-metal (TM)L2,3 edges are computed using the all-electron configuration interaction (CI) method. Slaterdeterminants for the CI calculations are composed of molecular orbitals obtained bydensity functional theory (DFT) calculations of model clusters. Relativistic effects aretaken into account by the zeroth-order regular approximation (ZORA) usingtwo-component wavefunctions. The theoretical spectra are found to be strongly dependenton the quality of the one-electron basis functions. On the other hand, a different choice ofthe exchange–correlation functionals for the DFT calculations does not exhibit visiblechanges in the spectral shape. Fine details of multiplet structures in the experimental TML2,3 XANES of MnO, FeO and CoO are well reproduced by the present calculations when theone-electron basis functions are properly selected. This is consistent with ourprevious report showing good agreement between theoretical and experimental TML2,3 XANES when four-component relativistic wavefunctions were used.

Molecular treatment of charge transfer in C2++He collisions. I. Ab initio evaluation of electronic energies and dynamical couplings

We present calculation of the electronic energies and dynamical couplings for the quasimolecule CHe2+, necessary to evaluate charge transfer cross sections in C2++He collisions. Using the MELD ab initio program, an all-electron configuration interaction method has been employed to calculate the molecular wavefunctions. The program has been modified to implement a numerical differentiation technique to evaluate the radial couplings. We discuss the usefulness of a one-electron picture to explain the mean features of the electronic-energies correlation diagrams. Electron translation factors have been included in the calculation of the (strongly origin-dependent) dynamical couplings.

Theoretical calculations on electronic transitions for H3, including Rydberg and transition state spectra

MRD-CI calculations have been carried out on the ground and excited electronic states of H3 for D3h, D∞h, C∞v, and C2v geometries. Dipole transition moments between the various electronic states have been also obtained at the different geometries calculated. The present work provides accurate theoretical information relevant to the transition state spectroscopy of H+H2 along a collinear path and also along a perpendicular path. In addition, the present work is the first all-electron configuration interaction treatment of the Rydberg states of H3, and the results are in excellent agreement with the observed spectra.