Extended coupled-cluster method. III. Zero-temperature hydrodynamics of a condensed Bose fluid

A coupled-cluster study of the ground-state energy and properties of an anisotropic quantum spin lattice model exhibiting antiferromagnetism in various phases

“…This quantity is defined (in the rotated Nrel basis) in Eq. (15). Thus, by inserting the SUB2 parametrizations of Eqs.…”

“…We recall further that this aspect implies that the CCM provides basically a biorthogonal (rather than an orthogonal) formulation of the quantum manybody problem. The explicit Hermitian conjugacy of the corresponding bra and ket vectors is thus not manifestly maintained at each level of approximation, for reasons that have been well described elsewhere [14,15,63,64]. Accordingly, we first describe in Sect.…”

The extended coupled cluster method and the pairing problem

“…The coupled cluster method has shown to be a very powerful technique to make such improvements, but we have little intuition what the best way to apply the method is. The work of Arponen [26] and Arponen and Bishop [27,28,29,30,31,32] provides one way; the use of Brueckner/maximum overlap orbitals [33], where we start from the BCS wave function, and express all corrections in terms of BCS quasiparticles, is an alternative.…”

Independent-cluster parametrizations of wave functions in model field theories. I. Introduction to their holomorphic representations

“…Furthermore, since in the ECCM (and only in the ECCM) all of the basic amplitudes obey the exact cluster property, this parametrization is capable in principle of describing such phenomena as phase transitions, states of topological excitation or deformation, and spontaneous symmetry breaking. Particular applications to date have included gauge-field descriptions of both a charged impurity in a polarizable medium [35] (of relevance, for example, to the important experimental tool of positron annihilation in metals) and the zero-temperature hydrodynamics of a strongly-interacting condensed Bose fluid [36].…”