Variational Approach for Many-Body Systems at Finite Temperature.

摘要: We introduce an equation for density matrices that ensures a monotonic decrease of the free energy and reaches fixed point at Gibbs thermal. build variational approach many-body systems can be applied to broad class states, including all bosonic fermionic Gaussian, as well their generalizations obtained by unitary transformations, such polaron transformations in electron-phonon systems. apply it Holstein model on $20\ifmmode\times\else\texttimes\fi{}20$ $50\ifmmode\times\else\texttimes\fi{}50$ square lattices, predict phase separation between superconducting charge-density wave phases strong interaction regime.