posted on 2024-03-06, 15:09authored byThomas Gasevic, Julius B. Kleine Büning, Stefan Grimme, Markus Bursch
A benchmark set for
the computation of 207Pb nuclear
magnetic resonance (NMR) chemical shifts is presented. The PbS50 set includes conformer ensembles of 50 lead-containing
molecular compounds and their experimentally measured 207Pb NMR chemical shifts. Various bonding motifs at the Pb center with
up to seven bonding partners are included. Six different solvents
were used in the measurements. The respective shifts lie in the range
between +10745 and −5030 ppm. Several calculation settings
are assessed by evaluating computed 207Pb NMR shifts for
the use with different density functional approximations (DFAs), relativistic
approaches, treatment of the conformational space, and levels for
geometry optimization. Relativistic effects were included explicitly
with the zeroth order regular approximation (ZORA), for which only
the spin–orbit variant was able to yield reliable results.
In total, seven GGAs and three hybrid DFAs were tested. Hybrid DFAs
significantly outperform GGAs. The most accurate DFAs are mPW1PW with
a mean absolute deviation (MAD) of 429 ppm and PBE0 with an MAD of
446 ppm. Conformational influences are small as most compounds are
rigid, but more flexible structures still benefit from Boltzmann averaging.
Including explicit relativistic treatments such as SO-ZORA in the
geometry optimization does not show any significant improvement over
the use of effective core potentials (ECPs).