The shell model Monte Carlo (SMMC) method enables calculations in model spaces that are many orders of magnitude larger than those that can be treated by conventional methods, and is particularly suitable for the calculation of level densities in the presence of correlations. We review recent advances and applications of SMMC for the microscopic calculation of level densities. Recent developments include (i) a method to calculate accurately the ground-state energy of an odd-mass nucleus, circumventing a sign problem that originates in the projection on an odd number of particles, and (ii) a method to calculate directly level densities, which, unlike state densities, do not include the spin degeneracy of the levels. We calculated the level densities of a family of nickel isotopes 59−64Ni and of a heavy deformed rare-earth nucleus 162Dy and found them to be in close agreement with various experimental data sets.The shell model Monte Carlo (SMMC) method enables calculations in model spaces that are many orders of magnitude larger than those that can be treated by conventional methods, and is particularly suitable for the calculation of level densities in the presence of correlations. We review recent advances and applications of SMMC for the microscopic calculation of level densities. Recent developments include (i) a method to calculate accurately the ground-state energy of an odd-mass nucleus, circumventing a sign problem that originates in the projection on an odd number of particles, and (ii) a method to calculate directly level densities, which, unlike state densities, do not include the spin degeneracy of the levels. We calculated the level densities of a family of nickel isotopes 59−64Ni and of a heavy deformed rare-earth nucleus 162Dy and found them to be in close agreement with various experimental data sets.

Apr 1, 20143 citations

Comment on “Quantum Monte Carlo Evidence for Superconductivity in the Three-Band Hubbard Model in Two Dimensions”

H. Endres, Werner R. Hanke, Hans Gerd Evertz +1 more

In a recent Letter, Kuroki and Aoki [Phys. Rev. Lett. 76, 440 (1996)] presented quantum Monte-Carlo (QMC) results for pairing correlations in the three-band Hubbard model, which describes the Cu-d_{x^2-y^2} and O-p_{x,y} orbitals present in the CuO_2 planes of high-T_c materials. In this comment we argue that (i) the used parameter set is not appropriate for the description of high-T_c materials since it does not satisfy the minimal requirement of a charge-transfer gap at half-filling, and (ii) the observed increase in the d_{x^2-y^2} channel is dominantly produced by the pair-field correlations without the vertex part. Hence, the claim of evidence of ODLRO is not justified.In a recent Letter, Kuroki and Aoki [Phys. Rev. Lett. 76, 440 (1996)] presented quantum Monte-Carlo (QMC) results for pairing correlations in the three-band Hubbard model, which describes the Cu-d_{x^2-y^2} and O-p_{x,y} orbitals present in the CuO_2 planes of high-T_c materials. In this comment we argue that (i) the used parameter set is not appropriate for the description of high-T_c materials since it does not satisfy the minimal requirement of a charge-transfer gap at half-filling, and (ii) the observed increase in the d_{x^2-y^2} channel is dominantly produced by the pair-field correlations without the vertex part. Hence, the claim of evidence of ODLRO is not justified.

arXiv:cond-mat/9609219Physical Review LettersJan 6, 19976 citations

Dynamical structure functions from quantum Monte Carlo calculations of a proper integral transform

Alessandro Roggero, Francesco Pederiva, Giuseppina Orlandini

An ab initio method for determining the dynamical structure function of an interacting many-body quantum system has been devised by combining a generalized integral transform method with quantum Monte Carlo (QMC) methods. A kernel has been found that (i) lets the transform be calculable with QMC methods and (ii) is a representation of the $\ensuremath{\delta}$ function, allowing an inversion of the transform with a much higher predictive power than the inverse Laplace transform. As a first application, the excitation spectrum of bulk atomic ${}^{4}$ He has been computed, both in the low and intermediate momentum ranges. The peculiar form of the kernel allows us to predict, without using any model, both positions and widths of the collective excitations in the maxon-roton region, as well as the existence of the second collective peak. A prediction of the dispersion of the single-particle modes described by the incoherent part is also presented.An ab initio method for determining the dynamical structure function of an interacting many-body quantum system has been devised by combining a generalized integral transform method with quantum Monte Carlo (QMC) methods. A kernel has been found that (i) lets the transform be calculable with QMC methods and (ii) is a representation of the $\ensuremath{\delta}$ function, allowing an inversion of the transform with a much higher predictive power than the inverse Laplace transform. As a first application, the excitation spectrum of bulk atomic ${}^{4}$He has been computed, both in the low and intermediate momentum ranges. The peculiar form of the kernel allows us to predict, without using any model, both positions and widths of the collective excitations in the maxon-roton region, as well as the existence of the second collective peak. A prediction of the dispersion of the single-particle modes described by the incoherent part is also presented.

Physical Review BSep 13, 201321 citations

{}^{4}

He has been computed, both in the low and intermediate momentum ranges. The peculiar form of the kernel allows us to predict, without using any model, both positions and widths of the collective excitations in the maxon-roton region, as well as the existence of the second collective peak. A prediction of the dispersion of the single-particle modes described by the incoherent part is also presented.