Application of relativistic effective core potentials

Abstract

It is known that relativistic effect should be included for the obtaining proper properties of molecular system having heavy element. However, it is very limited in calculating included relativistic effects for many molecular systems. Relativistic effective core potential (RECP) is efficient method and this includes major relativistic effects. In this research, RECP theory is implemented DIRAC program for the ground and excited state calculation of various molecular systems. From this work, various theories with RECP are enabled and more efficient calculation is obtained for the molecules having symmetric group. For the test case, ground state properties are calculated. Several correlation effects toward molecular geometries and energies were calculated for the group 17 hydrides. The spin-orbit effect affects significantly for the group 17 hydride with heavy element. From the several correlation effects, new composite methods were proposed for the accurate energy. Previously proposed composite methodologies correct spin-orbit effect only for the light atoms. However, for the heavy elements, molecular spin-orbit effect should be considered as well. From this work, newly proposed composite methods using RECP theory enable both atomic and molecular spin-orbit effects. These enable obtaining accurate energies including heavy elements in periodic table. For the test case, binding energies of group 13 hydride dimers were calculated. The excited state energies were calculated within several theories with RECP. Several molecular systems were calculated using time-dependent density functional theory. In case of the iodine molecule, several methods were compared with RECP based excited state calculations. Within correlation method, excited state based all-electron calculations gave very similar results comparing to RECP based calculations. From the consideration of various theories above, RECP theory can be systematically applied various ground and excited state calcula...