The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. http://dspace-roma3.caspur.it:80 2013-05-19T08:05:10Z 2013-05-19T08:05:10Z Barone, Paolo Raimondi, Roberto Capone, Massimo Castellani, Claudio Fabrizio, Michele http://hdl.handle.net/2307/73 2011-12-22T13:34:34Z 2008-06-19T07:19:16Z

<Title>Gutzwiller scheme for electrons and phonons: The half-filled Hubbard-Holstein model</Title> <Authors>Barone, Paolo; Raimondi, Roberto; Capone, Massimo; Castellani, Claudio; Fabrizio, Michele</Authors> <Issue Date>2008-06-19T07:19:16Z</Issue Date> <Is part of>Physical Review B</Is part of> <Volume>77</Volume> <Pages>235115</Pages> <Abstract>We analyze the ground-state properties of strongly correlated electrons coupled with phonons by means of a generalized Gutzwiller wave function, which includes phononic degrees of freedom. We study in detail the paramagnetic half-filled Hubbard-Holstein model, where the electron-electron interaction can lead to a Mott transition and the electron-phonon coupling to a bipolaronic transition. We critically discuss the quality of the proposed wave function in describing the various transitions and crossovers that occur as a function of the parameters. Previous variational attempts are recovered as particular choices of the wave function, while keeping all the variational freedom allows to access regions of the phase diagram, otherwise inaccessible within previous variational approaches.</Abstract>

2008-06-19T07:19:16Z Barone, Paolo Raimondi, Roberto Capone, Massimo Castellani, Claudio Fabrizio, Michele http://hdl.handle.net/2307/76 2011-12-22T13:34:34Z 2007-07-20T08:20:21Z

<Title>Extended Gutzwiller wavefunction for the Hubbard-Holstein model</Title> <Authors>Barone, Paolo; Raimondi, Roberto; Capone, Massimo; Castellani, Claudio; Fabrizio, Michele</Authors> <Issue Date>2007-07-20T08:20:21Z</Issue Date> <Is part of>Europhysics Letters</Is part of> <Volume>79</Volume> <Pages>47003</Pages> <Abstract>We introduce a new type of Gutzwiller variational wave function for correlated electrons coupled to phonons, able to treat on equal footing electronic and lattice degrees of freedom. We benchmark the wave function in the infinite-U Hubbard-Holstein model away from half-filling on a Bethe lattice, where we can directly compare with exact results by the Dynamical Mean-Field Theory. For this model, we find that variational results agree perfectly well with the exact ones. In particular the wave function correctly describes the crossover to a heavy polaron gas upon increasing the electron-phonon coupling.</Abstract>

2007-07-20T08:20:21Z