Atomic charge and atomic dipole fluxes during stretching displacements in small molecules

Abstract

First, the convergence in values of dynamic quantities such as atomic charge flux and atomic dipole flux that take place in stretching displacements is investigated in this work by means of calculations with three basis sets (cc-pVDZ, cc-pVTZ and cc-pVQZ) and different theoretical methods (HF, MP2, MP4(SDQ) and CCSD). The charges were obtained from QTAIM, Mulliken and NPA formalisms while atomic dipoles are only calculated from QTAIM. We studied a group of simple diatomic and triatomic molecules with diverse chemical bonding character: HF, HCl, LiH, NaH, NaCl, LiF, NaF, BF, AlF, BeO, MgO, CO, ClF, HCN, HNC, OCS, CO2 and CS2. The data obtained indicate that these dynamic quantities show well-behaved convergence patterns except by those from Mulliken for some triatomic systems with increasing basis set size. Some relevant dependence of QTAIM fluxes was observed in HF and HNC when small basis sets are used but the results still converge when larger basis sets are employed. Moreover, charge fluxes from QTAIM are in nice accordance with chemical arguments while the other formalisms exhibit results that are not plausible in some cases. The most remarkable ones are noticed in highly ionic diatomic systems, which should present negligible charge flux values during bond stretching displacements around equilibrium geometries.