Towards the parameterisation of the Hubbard model for salts of BEDT-TTF: A density functional study of isolated molecules

We calculate the effective Coulomb repulsion between electrons/holes, U, and site energy for an isolated BEDT-TTF [bis(ethylenedithio)tetrathiafulvalene] molecule in vacuo. U=4.2 \pm 0.1 eV for 44 experimental geometries taken from a broad range of conformations, polymorphs, anions, temperatures, and pressures (the quoted `error' is one standard deviation). Hence we conclude that U is essentially the same for all of the compounds studied. This shows that the strong (hydrostatic and chemical) pressure dependence observed in the phase diagrams of the BEDT-TTF salts is not due to U. Therefore, if the Hubbard model is sufficient to describe the phase diagram of the BEDT-TTF salts there must be significant pressure dependence on the intramolecular terms in the Hamiltonian and/or the reduction of the Hubbard U due to the interaction of the molecule with the polarisable crystal environment. The renormalised value of U is significantly smaller than the bare value of the Coulomb integral: F_0=5.2\pm0.1 eV across the same set of geometries, emphasising the importance of using the renormalised value of U. The site energy (for holes), xi=5.0\pm0.2 eV, varies only a little more than U across the same set of geometries. However, we argue that this plays a key role in understanding the role of disorder in ET salts in general and in explaining the difference between the beta_L and beta_H phases of beta-(BEDT-TTF)_2I_3 in particular.Comment: 13 pages, 6 figures, also see animations at http://www.youtube.com/watch?v=3K2kP8hWpZI, http://www.youtube.com/watch?v=wIz1cRsSdEs and http://www.youtube.com/watch?v=bNzUBAS6AFM, Expanded discussion of renormalisation effects. To appear in J. Chem. Phy

The Advertising Handbook

The Advertising Handbook provides a critical introduction to advertising and marketing practices today. Contributions from leading international scholars and practitioners offer extended coverage of the contemporary shifts and pressures reshaping the marketing communications (or advertising and marketing) industries and their relationship to the consumer. Profiles and case studies illustrate innovation and diversification among advertising, marketing and public relations companies. Discussion questions aid learning and encourage debate about the activities and influence of advertising today. Revised edition of The advertising handbook, 2009

Phase field theory of interfaces and crystal nucleation in a eutectic system of fcc structure: I. Transitions in the one-phase liquid region

The published version of this Article can be accessed from the link below - Copyright @ 2007 American Institute of PhysicsThe phase field theory (PFT) has been applied to predict equilibrium interfacial properties and nucleation barrier in the binary eutectic system Ag-Cu using double well and interpolation functions deduced from a Ginzburg-Landau expansion that considers fcc (face centered cubic) crystal symmetries. The temperature and composition dependent free energies of the liquid and solid phases are taken from CALculation of PHAse Diagrams-type calculations. The model parameters of PFT are fixed so as to recover an interface thickness of approximately 1 nm from molecular dynamics simulations and the interfacial free energies from the experimental dihedral angles available for the pure components. A nontrivial temperature and composition dependence for the equilibrium interfacial free energy is observed. Mapping the possible nucleation pathways, we find that the Ag and Cu rich critical fluctuations compete against each other in the neighborhood of the eutectic composition. The Tolman length is positive and shows a maximum as a function of undercooling. The PFT predictions for the critical undercooling are found to be consistent with experimental results. These results support the view that heterogeneous nucleation took place in the undercooling experiments available at present. We also present calculations using the classical droplet model classical nucleation theory (CNT) and a phenomenological diffuse interface theory (DIT). While the predictions of the CNT with a purely entropic interfacial free energy underestimate the critical undercooling, the DIT results appear to be in a reasonable agreement with the PFT predictions.This work has been supported by the Hungarian Academy of Sciences under Contract No. OTKA-K-62588 and by the ESA PECS Contract Nos. 98005, 98021, and 98043

By The Light Of The Jungle Moon

[Verse 1]When the jungle trees are swaying, bending to the breezes, playing,After the sun goes down.Little monkey eyes are gleaming, little monkey hearts are dreaming,Down in Jungle town.Ev’ry eye is turned toward the eastern sky, they’re watching for the jungle noon.Watching for its beams of yellow, when the jungle moon is mellow,That’s the time when monkeys like to spoon. [Chorus]By the light of the jungle moon, in the treetops above,Monkey boy sings a loving tune to his own turtle dove.And he whispers “Sweet Monkey Maid, won’t you come out and spoon?Here’s where the bliss is, come get your kisses,By the light of the jungle moon.” [Verse 2]Listen to the awful clatter, monkeys wonder what’s the matter,There goes a monkey lad.Crashing through the jungle branches, close behind him taking chances,Comes Miss Monkey’s Dad.Seems as if her angry Papa saw him kiss her and he means to catch him soon,Whill the old man tries to find him, Monkey boy will steal behind him,Back where sweet Miss Monkey waits to spoon. [Chorus x2

By the Light of the Jungle Moon

https://digitalcommons.library.umaine.edu/mmb-vp/5169/thumbnail.jp

Haldane phase in the hubbard model at 2/3-filling for the organic molecular compound Mo3 S7 (dmit)3

We report the discovery of a correlated insulator with a bulk gap at 2/3 filling in a geometrically frustrated Hubbard model that describes the low-energy physics of Mo3S7(dmit)(3). This is very different from the Mott insulator expected at half-filling. We show that the insulating phase, which persists even for very weak electron-electron interactions (U), is adiabatically connected to the Haldane phase and is consistent with experiments on Mo3S7(dmit)(3)

Ferromagnetic Coulomb phase in classical spin ice

Spin ice is a frustrated magnetic system that at low temperatures exhibits a Coulomb phase, a classical spin liquid with topological order and deconfined excitations. This work establishes the presence of a Coulomb phase with coexisting ferromagnetic order in a microscopic model of classical spin ice subject to uniaxial lattice distortion. General theoretical arguments are presented for the presence of such a phase, and its existence is confirmed using Monte Carlo results. This example is used to illustrate generic properties of spin liquids with magnetic order, including deconfinement of monopoles, signatures in the neutron-scattering structure factor, and critical behavior at phase transitions. An analogous phase, a superfluid with spontaneously broken particle–hole symmetry, is demonstrated in a model of hard-core lattice bosons, related to spin ice through the quantum– classical correspondenc

Competition between disorder and exchange splitting in superconducting ZrZn_2

We propose a simple picture for the occurrence of superconductivity and the pressure dependence of the superconducting critical temperature, T_{SC}, in ZrZn_2. According to our hypothesis the pairing potential is independent of pressure, but the exchange splitting, E_{xc}, leads to a pressure dependence in the (spin dependent) density of states at the Fermi level, D_\sigma(\epsilon_F). Assuming p-wave pairing T_{SC} is dependent on D_\sigma(\epsilon_F) which ensures that, in the absence of non-magnetic impurities, T_{SC} decreases as pressure is applied until it reaches a minimum in the paramagnetic state. Disorder reduces this minimum to zero, this gives the illusion that the superconductivity disappears at the same pressure as ferromagnetism does.Comment: 7 pages, 4 figures, submitted to J. Phys. Cond. Ma