Molecular QTAIM Topology Is Sensitive to Relativistic Corrections

Abstract

The topology of the molecular electron density of benzene dithiol gold cluster complex Au4−S−C6H4−S′−Au′4 changed when relativistic corrections were made and the structure was close to a minimum of the Born–Oppenheimer energy surface. Specifically, new bond paths between hydrogen atoms on the benzene ring and gold atoms appeared, indicating that there is a favorable interaction between these atoms at the relativistic level. This is consistent with the observation that gold becomes a better electron acceptor when relativistic corrections are applied. In addition to relativistic effects, here, we establish the sensitivity of molecular topology to basis sets and convergence thresholds for geometry optimization.

A Topological Data Analysis perspective on noncovalent interactions in relativistic calculations

“…Even though the optimized geometries of the Au complex are slightly different than by Anderson et al, our analysis confirms the main conclusions of the cited work: additional pairs of critical points of ED (1‐saddles and 2‐saddles, interpreted as “RCPs” and “BCPs” , respectively) between Au and H nuclei appear for certain combinations of Hamiltonians, methods, basis sets, molecular geometries, and spin states, but they never appear in the nonrelativistic context.…”

“…On the right diagram, the extra saddle‐saddle pair is displayed in dark red (rightmost spheres). Its extremely low persistence indicates a very weak salience of the corresponding topological feature, questioning its interpretation as a hydrogen bond suggested in Anderson et al…”

“…Its geometry was obtained (without reoptimization) by removing atoms from the g1 model of Au 4 ─S─C 6 H 4 ─S′─Au′ 4 molecule, so that it contains only one gold atom linked by sulfur to the ethene group that replaced the benzene ring. As the positions of all nuclei in Au‐S‐CH‐CH 2 were preserved as in the original molecule and due to the lack of symmetry in Au 4 ‐S‐C 6 H 4 ‐S′‐Au′ 4 , this simplification resulted in two geometries of the small model (atom numbers in parenthesis, after Anderson et al)—Au(4)─S(1)─C(1)H─C(2)H(1)H (“a”) and Au(8)─S(2)─C(4)H─C(3)H(2)H (“b”), hence the nomenclature m‐a‐g1 and m‐b‐g1 , respectively.…”

“…In order to illustrate and further extend the idea of using TDA for interatomic interactions, we have chosen a molecular system studied recently by Anderson et al, Au 4 ‐S‐C 6 H 4 ‐S′‐Au′ 4 (Figure ), which is interesting in the context of gold‐sulfur and gold‐hydrogen interactions due to their ubiquity in metalorganic complexes and on interface—a proof of many faces of the fascinating chemistry of gold . A remarkable finding of the study of Anderson et al is that it characterized the emergence of NCIs between gold and hydrogen centers, using the Quantum Theory of Atoms‐In‐Molecules (QTAIM)…”

“…Molecular systems under study: Au 4 ─S─C 6 H 4 ─S′─Au′ 4 (left) and Au─S─CH─CH 2 (right). The numbering of selected Au and H centers is shown and is the same as by Anderson et al Color coding for atoms: Au—yellow, S—red, C—dark gray, H—light gray. Additional information is available at 10.5281/zenodo.3358788…”