Towards Amplified Probing of Weak Intermolecular Interactions on the External Surfaces of Molecular Capsules.

We report a sensitive method for comparing weak interactions between aryl rings located on the external surfaces of equilibrating homo- and heterodimeric capsules. Two identical self-complementary resorcin[4]arene tetrabenzoate molecules and one tetramethylammonium cation form in CDCl hydrogen-bonded homodimeric capsules whose exteriors are decorated with four tight pairs of weakly interacting aryl rings. The pair wise mixing of six different homodimers establishes their equilibria with the corresponding heterodimeric species in which two types of aryl rings exert on each other some gentle forces.

Revised values for the X23 benchmark set of molecular crystals.

We present revised reference values for cell volumes and lattice energies for the widely used X23 benchmark set of molecular crystals by including the effect of thermal expansion. For this purpose, thermally-expanded structures were calculated via the quasi-harmonic approximation utilizing three dispersion-inclusive density-functional approximations. Experimental unit-cell volumes were back-corrected for thermal and zero-point energy effects, allowing now a direct comparison with lattice relaxations based on electronic energies.

Towards hybrid density functional calculations of molecular crystals via fragment-based methods.

We introduce and employ two QM:QM schemes (a quantum mechanical method embedded into another quantum mechanical method) and report their performance for the X23 set of molecular crystals. We furthermore present the theory to calculate the stress tensors necessary for the computation of optimized cell volumes of molecular crystals and compare all results to those obtained with various density functionals and more approximate methods. Our QM:QM calculations with PBE0:PBE+D3, PBE0:PBE+MBD, and B3LYP:BLYP+D3 yield at a reduced computational cost lattice energy errors close to the ones of the parent hybrid density functional method, whereas for cell volumes, the errors of the QM:QM scheme methods are in between the generalized gradient approximation and hybrid functionals.

Development of Embedded and Performance of Density Functional Methods for Molecular Crystals.

We report an alternative quantum mechanical:quantum mechanical (QM:QM) method to the currently used periodic density functional calculations including dispersion and investigate its performance with respect to main structural and energetic properties of the X23 set of molecular crystals. By setting the goal of reproducing reference periodic BLYP+D3 values and by embedding BLYP+D3 into DFTB, we obtain results similar to those of periodic BLYP+D3-typically within 1-2% in lattice energies and ∼0.4% in cell volumes.

On the Existence of HeHe Bond in the Endohedral Fullerene Hе @C.

Twenty years have already been passed since the endohedral fullerene's void ceaselessly attracts attention of both, experimentalists and theoreticians, computational chemists and physicists in particular, who direct their efforts on computer simulations of encapsulating atoms and molecules into fullerene void and on unraveling the arising bonding patterns. We review recent developments on the endohedral He @C fullerene, on its experimental observation and on related computational works. The two latter are the main concerns in the present work: on the one hand, there experimentally exists the He dimer embedded into C void.

Strain in nonclassical silicon hydrides: An insight into the "ultrastability" of sila-bi[6]prismane (Si18 H12) cluster with the endohedrally trapped silicon atom, Si19 H12.

The recently postulated concept of "ultrastability" and "electron-deficient aromaticity" (Vach, Nano Lett 2011, 11, 5477; Vach, J Chem Theory Comput 2012, 8, 2088) in a sila-bi[6]prismane having an additional entrapped silicon atom, Si19 H12 , has been disproved on the basis of a careful analysis of the energetic characteristics related to the formation of this and other silicon hydrides. The central silicon atom in Si19 H12 is weaker bound to other silicon atoms than in conventional tetrahedral silanes; moreover, Si19 H12 possesses a significant amount of strain. The role of strain in the formation of the title compounds has been further rationalized by calculating the relative energies for the transformation to a half-planar conformation in methane and in silane and by calculating the respective strain energies.

Encapsulation of diatomic molecules in fullerene C60: implications for their main properties.

The endohedral complexes of diatomic guest molecules H2, N2, O2, F2, HF, CO, LiH, LiF, BN, and BeO with C60 have been characterized computationally by employing second-order Møller-Plesset (MP2) theory and its density-fitting local (DF-LMP2) variant. The interaction energies, equilibrium geometries, dipole moments and harmonic vibrational frequencies of these complexes have been systematically calculated. It was found that all guest molecules are stabilized inside the C60 cage, with the most pronounced stabilization effect (of about 50 kcal mol(-1)) observed for the polar covalent BeO and BN molecules.

Parameterization of Halogens for the Density-Functional Tight-Binding Description of Halide Hydration.

Parameter sets of the self-consistent-charge density-functional tight-binding model with and without its third-order extension have been developed to describe the interatomic interactions of halogen elements (X = Cl, Br, I) with hydrogen and oxygen, with the ultimate goal of investigating halide hydration with this approach. The reliability and accuracy of the model with these newly developed parameters has been evaluated by comparing the structural, energetic, and vibrational properties of small molecules containing halogen atoms with those obtained by means of standard density-functional theory. Furthermore, the newly parametrized model is found to predict equilibrium geometries, binding energies, and vibrational frequencies for small aqueous clusters containing halogen anions, X(-)(H2O)n (n = 1-4), in good agreement with those calculated with density-functional theory and high-level ab initio quantum chemistry and with available experimental data.

An Improved Self-Consistent-Charge Density-Functional Tight-Binding (SCC-DFTB) Set of Parameters for Simulation of Bulk and Molecular Systems Involving Titanium.

A new self-consistent-charge density-functional tight-binding (SCC-DFTB) set of parameters for Ti-X pairs of elements (X = Ti, H, C, N, O, S) has been developed. The performance of this set has been tested with respect to TiO2 bulk phases and small molecular systems. It has been found that the band structures, geometric parameters, and cohesive energies of rutile and anatase polymorphs are in good agreement with the reference DFT data and with experiment.

Engineering crystals of dendritic molecules.

A detailed single-crystal X-ray study of conformationally flexible sulfonimide-based dendritic molecules with systematically varied molecular architectures was undertaken. Thirteen crystal structures reported in this work include 9 structures of the second-generation dendritic sulfonimides decorated with different aryl groups, 2 compounds bearing branches of both second and first generation, and 2 representatives of the first generation. Analysis of the packing patterns of 9 compounds bearing second-generation branches shows that despite their lack of strong directive functional groups there is a repeatedly reproduced intermolecular interaction mode consisting in an anchor-type packing of complementary second-generation branches of neighbouring molecules.

Toward an Accurate Density-Functional Tight-Binding Description of Zinc-Containing Compounds.

An extended self-consistent charge density-functional tight-binding (SCC-DFTB) parametrization for Zn-X (X = H, C, N, O, S, and Zn) interactions has been derived. The performance of this new parametrization has been validated by calculating the structural and energetic properties of zinc solid phases such as bulk Zn, ZnO, and ZnS; ZnO surfaces and nanostructures; adsorption of small species (H, CO2, and NH3) on ZnO surfaces; and zinc-containing complexes mimicking the biological environment. Our results show that the derived parameters are universal and fully transferable, describing all the above-mentioned systems with accuracies comparable to those of first-principles DFT results.

Calculations of the C2 fragmentation energies of higher fullerenes C80 and C82.

The C2 fragmentation energies of the most stable isolated-pentagon-rule (IPR) isomers of the C80 and C82 fullerenes were evaluated with second-order Møller-Plesset (MP2) theory, density-functional theory (DFT) and the semiempirical self-consistent charge density-functional tight-binding (SCC-DFTB) method. Zero-point energy, ionization energy and empirical C2 corrections were included in the calculation of fragmentation energies for comparison with experimental C2 fragmentation energies of the fullerene cations. In the case of the most probable Stone-Wales pathway of C2 fragmentation of C80, the calculated [Formula: see text] agree well with experimental data, whereas in the case of C(82) fragmentation, the calculated [Formula: see text] exceed by up to 1.

Toward a reversible isolation of a C20 fullerene inside a tetraureacalix[4]arene dimer. A theoretical study.

The potential stabilization of normally unstable C20, the smallest fullerene, via its encapsulation inside a tetraureacalix[4]arene dimer has been analyzed using molecular mechanics calculations with different force fields, the self-consistent-charge density-functional tight-binding with dispersion correction (SCC-DFTB-D) model, and standard density-functional-theory (DFT) calculations. The interaction energies obtained for the C20 complex have been compared with analogous values calculated for numerous complexes of the tetraureacalix[4]arene dimer with other guests. Results of the calculations with all force fields and SCC-DFTB-D predict that the binding of C20 occurs with the highest selectivity.

Water solubilization, determination of the number of different types of single-wall carbon nanotubes and their partial separation with respect to diameters by complexation with eta-cyclodextrin.

Complexation of single-wall carbon nanotubes with 12-membered cyclodextrins enables not only their solubilization in water but also their partial separation with respect to diameters and determination of the number of nanotube types on the basis of NMR spectra.