The formalism based on the total energy bifunctional (E[ρI,ρII]) is used to derive interaction energies for several hydrogen-bonded complexes (water dimer, HCN–HF, H2CO–H2O, and MeOH–H2O). Benchmark ab initio data taken from the literature were used as a reference in the assessment of the performance of gradient-free [local density approximation (LDA)] and gradient-dependent [generalized gradient approximation (GGA)] approximations to the exchange-correlation and nonadditive kinetic-energy components of E[ρI,ρII]. On average, LDA performs better than GGA. The average absolute error of calculated LDA interaction energies amounts to 1.0kJ∕mol. For H2CO–H2O and H2O–H2O complexes, the potential-energy curves corresponding to the stretching of the intermolecular distance are also calculated. The positions of the minima are in a good agreement (less than 0.2Å) with the reference ab initio data. Both variational and nonvariational calculations are performed to assess the energetic effects associated with complexation-induced deformations of molecular electron densities.

Two novel hybrid organic–inorganic perovskites, pyridinium lead tribromide and pyridinium lead triiodide, are prepared. Based on the XRD data, we find that the compounds are quasi-one-dimensional crystals of Pna21 symmetry. DFT calculations demonstrate that the valence band of the new compounds is comprised of the occupied p-orbitals of the halogen anions, while their conduction bands CB and CB + 1 are composed mainly of the unoccupied π-orbitals of the aromatic pyridinium rings. The computed DOS matches well with the recorded XPS spectra. The pyridinium lead tribromide and pyridinium lead triiodide absorption peaks derived from the experimental DRS are located at ∼3.1 eV and ∼2.4 eV, respectively. An agreement between the experimentally and theoretically predicted absorption spectra is found. The synthesized compounds extend the range of quasi-one-dimensional organometallic perovskites suitable for optical and possibly electronic applications.