Electric Field Gradient in Chiral and Tetrahedral Molecules within High-Order LRESC Formalism

In this work, we present the electric
field gradient
(EFG) given
by the linear response elimination of the small component (LRESC)
scheme up to the 1/c4 order (c is the speed of light in vacuum) in CHFClX (X = Br, I, At) chiral
molecules, together with CHF2Br and CH2FX (X
= Br, I, At) tetrahedral systems. The former could be good candidates
for further parity violation studies, especially when heavy atoms
are surrounding. In this context, the LRESC scheme demonstrates effective
applicability to large tetrahedral and chiral molecules that incorporate
heavy elements, with relativistic effects playing a crucial role.
The LRESC results of EFG exhibit an excellent agreement with those
calculated at the four-component level, giving differences of only
hundredths order in a.u. (atomic units) for the bromine nucleus and
less than 0.1 a.u. for the iodine nucleus. Regarding the other nuclei,
for the chiral molecules, there is a heavy atom effect on the light
atom (HALA) for chlorine and fluorine atoms as the substituent halogen
atom becomes heavier. Furthermore, the electronic part of the EFG
for the central carbon and the fluorine nuclei presents an important
dependence with the environment in the molecules under study. With
accurate calculations of the EFG and tabulated nuclear quadrupole
moment, the nuclear quadrupole coupling constant is obtained within
the LRESC scheme, including for the first time correlation effects
on the spin-dependent corrections with this methodology, providing
results close to the experimental ones for Cl, Br, and I atoms. At
the Hartree–Fock level, the differences are around 6% for Br
and I nuclei, and at the density functional theory level with the
LDA and PBE0 functionals, the differences are no more than 2%.