arXiv subjects

J. Casulleras

Publications and source records attributed to J. Casulleras.

41 records · Page 3Linked to original sources

arXiv1995

Diffusion Monte Carlo study of two-dimensional liquid $^4$He

The ground-state properties of two-dimensional liquid $^4$He at zero temperature are studied by means of a quadratic diffusion Monte Carlo method. As interatomic potential we use a revised version of the HFDHE2 Aziz potential which is expected to give a better description of the interaction between helium atoms. The equation of state is determined with great accuracy over a wide range of densities in the liquid phase from the spinodal point up to the freezing density. The spinodal decomposition density is estimated and other properties of the liquid, such as radial distribution function, static form factor, momentum distribution and density dependence of the condensate fraction are all presented.

cond-mat↗

arXiv1995

Bounds for the phonon-roton dispersion in superfluid 4He

The sum rule approach is used to derive upper bounds for the dispersion law $ω_0(q)$ of the elementary excitations of a Bose superfluid. Bounds are explicitly calculated for the phonon-roton dispersion in superfluid $^4$He, both at equilibrium ($ρ=0.02186$ Å$^{-3}$) and close to freezing ($ρ=0.02622$ Å$^{-3}$). The bound $ω_0(q) \le 2S(q)\midχ(q)\mid^{-1}$, where $S(q)$ and $χ(q)$ are the static structure factor and density response respectively, is calculated microscopically for several values of the wavevector $q$. The results provide a significant improvement with respect to the Feynman approximation $ω_F(q)= q^2(2mS(q))^{-1}$. A further, stronger bound, requiring the additional knowledge of the current correlation function is also investigated. New results for the current correlation function are presented.

cond-mat↗

arXiv1995

Unbiased estimators in Quantum Monte Carlo methods: application to liquid $^4$He

A Monte Carlo algorithm for computing quantum mechanical expectation values of coordinate operators in many body problems is presented. The algorithm, that relies on the forward walking method, fits naturally in a Green's Function Monte Carlo calculation, i.e., it does not require side walks or a bilinear sampling method. Our method evidences stability regions large enough to accurately sample unbiased pure expectation values. The proposed algorithm yields accurate results when it is applied to test problems as the hydrogen atom and the hydrogen molecule. An excellent description of several properties of a fully many body problem as liquid $^4$He at zero temperature is achieved.

cond-mat↗

arXiv1994

Monte Carlo Calculations for Liquid $^4$He at Negative Pressure

A Quadratic Diffusion Monte Carlo method has been used to obtain the equation of state of liquid $^4$He including the negative pressure region down to the spinodal point. The atomic interaction used is a renewed version (HFD-B(HE)) of the Aziz potential, which reproduces quite accurately the features of the experimental equation of state. The spinodal pressure has been calculated and the behavior of the sound velociy around the spinodal density has been analyzed.

cond-mat↗

arXiv1993

Monte Carlo Analysis of a New Interatomic Potential for He

By means of a Quadratic Diffusion Monte Carlo method we have performed a comparative analysis between the Aziz potential and a revised version of it. The results demonstrate that the new potential produces a better description of the equation of state for liquid $^4$He. In spite of the improvement in the description of derivative magnitudes of the energy, as the pressure or the compressibility, the energy per particle which comes from this new potential is lower than the experimental one. The inclusion of three-body interactions, which give a repulsive contribution to the potential energy, makes it feasible that the calculated energy comes close to the experimental result.

cond-mat↗