The SE100 database
collecting accurate equilibrium geometries of
medium size molecules obtained by the semiexperimental (SE) approach
has been extended to species containing Br and I atoms. This has allowed
the determination of accurate linear regressions between DFT and SE
values for all the main bonds and angles involving H, B, C, N, O,
F, P, S, Cl, Br, and I atoms. An improved Nano-LEGO tool has been
developed, which is based on suitable hybrid and double hybrid functionals
and combines in a fully coherent way the templating molecule and linear
regression approaches. A number of case studies show that the new
Nano LEGO tool provides geometrical parameters on par with state-of-the-art
composite wave function methods, but can be routinely applied to medium-
to large-size molecules. The accuracy reached for structural parameters
is mirrored on rotational constants that can be predicted with an
average error within 0.2%.