Neel-state-based ansatze

Therefore, two main different kinds of variational localized-site cluster expanded ansatze have so far been considered first the Neel-state-based ansatze (NSBA), where the Neel state is the zero order wave-function from which the trial wave-functions are generated, and second the Resonating... 

Three-Bond-Range RVB ansatze Following a strategy parallel to that of the Neel-state based ansatze, we try to generate a trial wave function as a superposition, now, of singlets which are obtained from a cluster-... 

Neel-State-Based Ansatz The NSBA of Subsec. 4.1, with M = 2 and M = 4, and alternate translational symmetry conditions, has been used [34] to obtain the energy as a function of the variational parameters and the interatomic distances, rq and r 2- Upon optimization, the geometry and the alternating-to-regular geometry transition have been obtain (see Ref. 34). 

Table 2 Results of Variational Localized-site Cluster expansions from either a Neel-state based ansatze or a Resonating Valence Bond ansatz. We notice that the lower level NSBA is unable of showing the dimerization of polyacetylene. rc is the critical bifurcation mean bond length, r and r2 are the optimized short and long bond distances (in A). E is the energy per carbon atom (in eV), taking the energy of the Neel state with 1.40 A equal bond lengths as zero of energy. NSB forth order perturbative and Dimer-covering second order perturbative (see Ref. 34), CEPA ab-initio estimate of Kpnig and Stollhoff [52], and the experimental results [46,47] for rx and r2 have been added for comparison.

THE NEEL-STATE-BASED CLUSTER-EXPANDED ANSATZE... 

Table 3 Optimized regular interatomic distance (in A) and gain in energy per C2H2 unit (in eV) of regular polyacetylene by report to the alternating ground state, with the Neel state based higher order and the RVB ansatze. Results from Local-density-functional approach of Mintmire and White [48], Hartree-Fock and Mpller-Plesset perturbation Theory of Suhai [50], or Ashkenazi [49] are included.

The cluster expanded wave-function ansatze in this section are based upon the Neel state as a zero-order wave-function,... 

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