Classical Analogue of the Ionic Hubbard Model

In our earlier work [M. Hafez, {\em et al.}, Phys. Lett. A {\bf 373} (2009) 4479] we employed the flow equation method to obtain a classic effective model from a quantum mechanical parent Hamiltonian called, the ionic Hubbard model (IHM). The classical ionic Hubbard model (CIHM) obtained in this way contains solely Fermionic occupation numbers of two species corresponding to particles with \up and \down spin, respectively. In this paper, we employ the transfer matrix method to analytically solve the CIHM at finite temperature in one dimension. In the limit of zero temperature, we find two insulating phases at large and small Coulomb interaction strength, $U$, mediated with a gap-less metallic phase, resulting in two continuous metal-insulator transitions. Our results are further supported with Monte Carlo simulations.Comment: 12 figure

A modified least squares formulation for a system of first order equations

Second order equations in terms of auxiliary variables similar to potential and stream functions are obtained by applying a weighted least squares formulation to a first order system. The additional boundary conditions which are necessary to solve the higher order equations are determined and numerical results are presented for the Cauchy-Riemann equations

Conductance of S-Alkylisothiouronium Iodides in Methanol at 25° C

Equivalent conductivities are reported for S-Methyl-, S-n- . -Butyl, S-n-Amyl- and S-n-Heptylisothiouronium iodides in methanol (D = 32.63) at 25 °c. The data were analyzed by the Fuoss-Onsager equation for 1 : 1 associated electrolytes. The characteristic constants: the equivalent conductance at infinite dilution A0 , the closest approach distance a0 and the association constant KA are · derived

Excitation Spectrum of One-dimensional Extended Ionic Hubbard Model

We use Perturbative Continuous Unitary Transformations (PCUT) to study the one dimensional Extended Ionic Hubbard Model (EIHM) at half-filling in the band insulator region. The extended ionic Hubbard model, in addition to the usual ionic Hubbard model, includes an inter-site nearest-neighbor (n.n.) repulsion, $V$. We consider the ionic potential as unperturbed part of the Hamiltonian, while the hopping and interaction (quartic) terms are treated as perturbation. We calculate total energy and ionicity in the ground state. Above the ground state, (i) we calculate the single particle excitation spectrum by adding an electron or a hole to the system. (ii) the coherence-length and spectrum of electron-hole excitation are obtained. Our calculations reveal that for V=0, there are two triplet bound state modes and three singlet modes, two anti-bound states and one bound state, while for finite values of $V$ there are four excitonic bound states corresponding to two singlet and two triplet modes. The major role of on-site Coulomb repulsion $U$ is to split singlet and triplet collective excitation branches, while $V$ tends to pull the singlet branches below the continuum to make them bound states.Comment: 10 eps figure

From Gapped Excitons to Gapless Triplons in One Dimension

Often, exotic phases appear in the phase diagrams between conventional phases. Their elementary excitations are of particular interest. Here, we consider the example of the ionic Hubbard model in one dimension. This model is a band insulator (BI) for weak interaction and a Mott insulator (MI) for strong interaction. Inbetween, a spontaneously dimerized insulator (SDI) occurs which is governed by energetically low-lying charge and spin degrees of freedom. Applying a systematically controlled version of the continuous unitary transformations (CUTs) we are able to determine the dispersions of the elementary charge and spin excitations and of their most relevant bound states on equal footing. The key idea is to start from an externally dimerized system using the relative weak interdimer coupling as small expansion parameter which finally is set to unity to recover the original model.Comment: 18 pages, 10 figure

Simple approach to thieno[3,2-d]pyrimidines as new scaffolds of antimicrobial activities

6-(4-Chlorophenyl)-spiro[cyclohexane-1,2-thieno[3,2-d][1,3]oxazin]-4(1H)-one (1) was synthesized and used as a starting material for the synthesis of a novel series of spiro compounds having biologically active sulfonamide (2a-e) and 3-(4-acetylphenyl)-6-(4-chlorophenyl)-1H-spiro[cyclohexane-1,2-thieno[3,2-d]pyrimidine-4(3H)-one (3). Compound 2a was used as a key intermediate for the synthesis of sulfonyl carbothioamide derivatives (4a-c). Also, compound 3 was used as an intermediate for the synthesis of 3H-spiro[cyclohexane-1,2-thieno[3,2-d]pyrimidin]-3-yl]phenyl}-2-imino-4-(substituted phenyl and/or thienyl)-1,2-dihydropyridine-3-carbonitrile derivatives (5a-e), 3H-spiro[cyclohexane-1,2-thieno[3,2-d]pyrimidin]-3-yl]phenyl}-2-oxo-4-(substituted phenyl and/or thienyl)-1,2-dihydropyridine-3-carbonitrile derivatives (6a-e), and 4-[(2Z)-3-substituted-arylprop-2-enoyl]phenyl-1H-spiro[cyclohexane-1,2-thieno[3,2-d]pyrimidine derivatives (7a-e). Cyclocondensation of 7a-e with hydrazine hydrate produced 6-(4-chlorophenyl)-3-[4-(5-substituted aryl-4,5-dihydro-1H-pyrazol-3-yl)phenyl]-1H-spiro[cyclohexane-1,2-thieno-[3,2-d]pyrimidin]-4(3H)-ones (8a-e), but with hydroxylamine hydrochloride afforded the corresponding isoxazoline derivatives (9a-e). Also, cyclocondensation by thiourea afforded 2-thioxo-1,2-dihydropyrimidin-4-yl)-phenyl-spiro-{cyclohexanethieno[3,2-d]pyrimidin}-4-one derivatives (10a-e). The new compounds were investigated for antimicrobial activity. Compounds 2c, 8b, c, 9b and 10b were the most potent ones against both Gram-negative and Gram-positive bacteria. Compound 8c exhibited higher antifungal activity towards the examined fungi with MIC of 1–2 µmol mL–1 compared to ketoconazole (MIC 2–3 µmol mL–1)