A note on the importance of d orbitals in the calculation of effective interactions and the excitation spectra of atoms and molecules

The focal point of our discussion is the examination of truncated basis sets used in obtaining an accurate first principles clculation of the effective valence shell Hamiltonian by the canonical transformation-cluster expansion approasch. Subsequent diagonalization of this effecitve valence shell hamiltonian yields the valence shell transition energies. A detailed analysis of numerical results obtained using a number of different basis sets of hydrogen-like orbitals together with rigorous symmetry arguments celarly demonstrates the special role played by d orbitals in computing the ³P → ¹D transition energy in carbon. The failure of early attempts to calculate the effective Hamiltonian for ethylene from first principles is examined in the light of recent ab initio calculations on ethylene involving d orbitals and the computations reported in this paper. We conclude that accurate calculations of the effective valence shell Hamiltonian for molecules must consider d orbitals in the excited orbital basis set.     

Utilization of 1-oxa-2,2-(dimesityl)silacyclopentane acetals in the stereoselective synthesis of polyols

We have developed a route for the stereoselective synthesis of 1-oxa-2,2-(dimesityl)silacyclopentane acetals, intermediates in the synthesis of highly functionalized 1,3-diols. This route involves a diastereoselective conjugate addition reaction of a hydrosilyl anion, a subsequent diastereoselective enolate alkylation, and a fluoride-catalyzed intramolecular hydrosilylation reaction to afford the oxasilacyclopentane acetal. A highly selective nucleophilic substitution reaction, followed by oxidation of the C-Si bond, leads to the desired polyol.     

Magnetoelectric compounds with two sets of magnetic sublattices: UCrO4 and NdCrTiO5

Using magnetic and magnetoelectric (ME) powder susceptibility measurements, the low temperature magnetic properties of antiferromagnetic UCrO₄ and NdCrTiO₅ have been studied. Their Néel temperatures T_N are 44.5 and 20.5°K, respectively, the Cr³⁺ spin systems of both materials ordering cooperatively at T_N. Below T_N, the U⁵⁺ and Nd³⁺ moments are polarized due to their exchange interaction with the ordered Cr³⁺ spins. It is argued that, for both compounds, each of the two spin systems contributes to the ME susceptibilities. They are thus the first known ME materials possessing two distinct magnetic sublattices. The effective magnetic moments calculated from the magnetic susceptibilities are in good agreement with those previously reported by neutron diffraction studies.     

Adiabatic ionization energies from charge transfer equilibrium constants; experimental determinations of entropy changes for charge transfer equilibria

Equilibrium constants have been measured as a function of temperature for the charge transfer equilibria in mixtures of NO with aromatic compounds, and mixtures of aromatic compounds. The experimentally determined entropy changes are in good agreement with entropy changes calculated from statistical mechanical considerations provided an intermolecular component is included. The enthalpy changes for the charge transfer reactions correspond to the differences in the adiabatic ionization potentials of the compounds.     

Self-Assembled Multistable Scattering Mode for Versatile Energy-Saving Smart Windows

Smart windows are crucial to dynamic control over light transmission to fulfill various demands in energy saving, privacy, and information display; however, most present technologies still perform a single function (often tint or haze adjustment) and require continuous electricity for operation. In this study, novel self-assembled ionic liquid crystals (ILCs) doped with negative cholesteric liquid crystals (CLCs) to offer electrically switchable and stable scattering-mode light modulators are presented. The novel smectic A phase based on the ILCs exhibits high solubility in the adopted nematics, enhancing the LC device's performance in several ways, including improved homogeneity, stable alignment quality, prolonged stability, and simplified fabrication. The LC device can potentially offer a dynamically rapid switching function between stable transparent (imperfect fingerprint textures) states and stable scattering (focal conic textures with small domains) states by using external stimuli and highly maintained multistable states for prolonged periods, even when the external stimuli are removed. The LC device also offers polarization-independent scattering and transparent-mode LC light modulators, low operating voltage, excellent contrast, and broad viewing angles. Its versatility and outstanding field-off stability make it ideal for various applications such as smart lighting, building climate control, energy-saving displays, and augmented reality (AR) glasses.     

A study of structural, compositional and optical properties of spray-deposited non-stoichiometric (Zn,Fe)S thin films

Non-stoichiometric ternary chalcogenides (Zn,Fe)S were prepared in the film form by pyrolytic spray deposition technique, using air/nitrogen as the carrier gas. The precursor solution comprised of ZnCl₂, FeCl₂ and thiourea. The depositions were carried out under optimum conditions of experimental parameters viz. carrier gas (air/nitrogen) flow rate, concentration of precursor constituents, nozzle substrate distance and temperature of quartz substrate. The deposited thin films were later sintered in argon at 1073 K for 120 min.The structural, compositional and optical properties of the sintered thin films were studied. X-ray diffraction studies of the thin films indicated the presence of (Zn,Fe)S solid solution with prominent cubic sphalerite phase while surface morphology as determined by scanning electron microscopy (SEM) revealed a granular structure.The chemical composition of the resulting thin films as analyzed by energy dispersive X-ray analysis (EDAX) reflected the composition of the precursor solutions from which the depositions were carried out with Fe at% values ranging from 0.4 up to 33.SEM micrographs of thin films reveal that the grain sizes of the thin films prepared using air as carrier gas and N₂ as carrier gas are in the vicinity of 300 and 150 nm, respectively.The diffuse transmittance measurements for thin films, as a function of wavelength reveal the dependence of direct optical band gap on Fe content and type of phase.     

Combinatorial synthesis of small-molecule libraries using 3-amino-5-hydroxybenzoic acid

Summary A non-peptide library of 2001 compounds has been prepared utilizing solid-phase techniques. The split/combine method was demonstrated to work well to form mixtures of compounds based on 3-amino-5-hydroxybenzoic acid as a core structure. The benzoic acid of the core structure served as the attachment point for the resin and the amino and hydroxy positions were variably substituted.