Towards High Performance Relativistic Electronic Structure Modelling: The EXP-T Program Package

Modern challenges arising in the fields of theoretical and experimental physics require new powerful tools for high-precision electronic structure modelling; one of the most perspective tools is the relativistic Fock space coupled cluster method (FS-RCC). Here we present a new extensible implementation of the FS-RCC method designed for modern parallel computers. The underlying theoretical model, algorithms and data structures are discussed. The performance and scaling features of the implementation are analyzed. The software developed allows to achieve a completely new level of accuracy for prediction of properties of atoms and molecules containing heavy and superheavy nuclei

Large Shape Staggering in Neutron-Deficient Bi Isotopes

The changes in the mean-square charge radius (relative to Bi-209), magnetic dipole, and electric quadrupole moments of Bi-187,Bi-188,Bi-189,Bi-191 were measured using the in-source resonance-ionization spectroscopy technique at ISOLDE (CERN). A large staggering in radii was found in Bi-187,188,189(g), manifested by a sharp radius increase for the ground state of Bi-188 relative to the neighboring Bi-187,189(g). A large isomer shift was also observed for Bi-188(m). Both effects happen at the same neutron number, N = 10(5), where the shape staggering and a similar isomer shift were observed in the mercury isotopes. Experimental results are reproduced by mean-field calculations where the ground or isomeric states were identified by the blocked quasiparticle configuration compatible with the observed spin, parity, and magnetic moment.Peer reviewe