Approaching the bulk limit with finite cluster calculations using local increments: the case of LiH

Finite-cluster calculations employing high-level wavefunction-based ab initio methods and extended atomic-orbital basis sets are used to determine local energy increments for bulk LiH. It is shown that these increments can be converged with respect to cluster size and point-charge embedding so as to yield bulk cohesive energies with an accuracy of better than 1 mE(h), both at the Hartree-Fock and at correlated levels. Instrumental for the efficiency of the scheme is the introduction of non-orthogonal orbitals, at an intermediate stage.     

Sterically Active Electron Pairs in Lead Sulfide? An Investigation of the Electronic and Vibrational Properties of PbS in the Transition Region Between the Rock Salt and the α‐GeTe‐Type Modifications

Recently, we have investigated the energy landscape of PbS for many different pressures on the ab initio level by using Hartree–Fock and density functional theory to globally search for possible thermodynamically stable and metastable structures. The perhaps most fascinating observation was that besides the experimentally known modification exhibiting the rock salt structure a second minimum exists close‐by on the landscape showing the low‐temperature α‐GeTe‐type structure. In the present study, we investigate the possible reasons for the existence of this metastable modification; in particular we address the question, whether the α‐GeTe‐type modification might be stabilized (and conversely the rock salt modification destabilized) by steric effects of the non‐bonding electron pair.     

First principles study of structural stability, electronic and related properties of (NH4)2SO4

The electronic structure and related physical properties of crystalline ammonium sulfate, (NH₄)₂SO₄, have been studied using the first principles code CRYSTAL06 at the B3LYP level of theory. The title compound has been found to possess one stable and three metastable configurations, all within the polar space group Pna2₁ (no. 33). Two of the metastable polymorphs are newly predicted and have not yet been observed experimentally. The different configurations show considerably varying magnitudes of the spontaneous polarization P_s. All coefficients of the elastic stiffness tensor, c_kl, and elasto-electrical tensor, e_ki have been calculated for the first time and have been found to agree satisfactorily with experimental data, as far as available.     

Solvent‐free polymerization of citric acid and D‐sorbitol

Copolymers of citric acid and D ‐sorbitol were synthesized with a solvent‐free vacuum‐oven synthesis with molar ratios of citric acid to D ‐sorbitol ranging from 1/1 to 6/1. The extent of the reaction was followed by the monitoring of the residual acid content of the system. As expected, the reaction occurred much more rapidly at 150 than at 110 °C. The Fourier transform infrared (FTIR) spectra of the products showed the expected FTIR bands at approximately 1735 and 1188 cm^?1, which were indicative of ester formation. Gel permeation chromatography showed a major product with a molecular weight of approximately 3500 Da. An insoluble material with a water‐absorption index of up to 17 was also synthesized and could lead to possible applications as absorbers, thickeners, and biobased seed coatings. Additionally, the mono‐ and disodium salts of citric acid were also polymerized with D ‐sorbitol in a manner similar to that of the citric acid system. Soluble polymers were synthesized with a residual acid content of 5 mequiv/g of polymer. These materials showed Ca⁺²‐sequestering ability (up to 0.56 mmol of Ca⁺²/g of the product). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4259–4267, 2006