Machine-learning of atomic-scale properties based on physical principles

We briefly summarize the kernel regression approach, as used recently in materials modelling, to fitting functions, particularly potential energy surfaces, and highlight how the linear algebra framework can be used to both predict and train from linear functionals of the potential energy, such as the total energy and atomic forces. We then give a detailed account of the Smooth Overlap of Atomic Positions (SOAP) representation and kernel, showing how it arises from an abstract representation of smooth atomic densities, and how it is related to several popular density-based representations of atomic structure. We also discuss recent generalisations that allow fine control of correlations between different atomic species, prediction and fitting of tensorial properties, and also how to construct structural kernels---applicable to comparing entire molecules or periodic systems---that go beyond an additive combination of local environments

Unexpected chalcogen bonds in tetravalent sulfur compounds

In this manuscript we have combined a CSD (Cambridge Structural Database) analysis with theoretical calculations (RI-MP2/def2-TZVP level of theory) to study the importance of polarizability in chalcogen bonding interactions. It is well known that chalcogen bonds are stronger for less electronegative chalcogen atoms, i.e., S < Se < Te, and in the presence of electron-withdrawing substituents at the chalcogen. Herein, we report experimental and theoretical evidence (RI-MP2/def2-TZVP) that the chalcogen bond acceptor (Lewis base) has a preference in some cases for the σ-hole that is opposite to the more polarizable group instead of the more electron withdrawing one, as confirmed by Natural Bond Orbital (NBO) and Bader's theory of "atoms-in-molecules" computational tools

New 1,8-naphthyridine-based probes for the selective fluorescence signalling of toxic cadmium: synthesis, photophysical studies and molecular modelling

[eng] Newly synthesised 1,8-naphthyridine-based molecular probes, NAP-1 and NAP-2, exhibit highly selective fluorescence responses towards the toxic cadmium over coordinatively competing Zn2+ and several other metal ions examined. On the one hand, NAP-1 (MeOH:H2O, v/v 80:20, pH 7.4) exhibits ca. 1.5 order of magnitude higher stability constant for Cd2+ over Zn2+; on the other hand, NAP-2 in MeOH offers unique selectivity only towards Cd2+, exhibiting both absorbance and emission red shifts as well as fluorescence enhancement. By 1H NMR analysis, the tetra-coordinated binding is indicated at least for the NAP-1+Cd2+ complex and theoretical calculations reveal relatively stronger binding of Cd2+ over Zn2+