IFIBA   22255
INSTITUTO DE FISICA DE BUENOS AIRES
Unidad Ejecutora - UE
artículos
Título:
Simulations of Cold Nuclear Matter at sub-saturation densities
Autor/es:
PEDRO A. GIMÉNEZ MOLINELLI; JUAN I. NICHOLS; JORGE A. LÓPEZ; CLAUDIO O. DORSO
Revista:
NUCLEAR PHYSICS A
Editorial:
ELSEVIER SCIENCE BV
Referencias:
Lugar: Amsterdam; Año: 2014 vol. 923 p. 31 - 50
ISSN:
0375-9474
Resumen:
Ideal nuclear matter is expected to undergo a first order phase
transition at the thermodynamic limit. At such phase transitions the
size of density fluctuations (bubbles or droplets) scale with the size
of the system. This means that simulations of nuclear matter at
sub-saturation densities will inexorably suffer from what is vaguely
referred to as ?finite size effects?. It is usually thought that these
finite size effects can be diminished by imposing periodic boundary
conditions and making the system large enough, but as we show in this
work, that is actually not the case at sub-saturation densities. In this
paper we analyze the equilibrium configurations of molecular dynamics
simulations of a classical model for symmetric ideal (uncharged) nuclear
matter at sub-saturation densities and low temperatures, where phase
coexistence is expected at the thermodynamic limit. We show that the
most stable configurations in this density range are almost completely
determined by artificial aspects of the simulations (i.e. boundary
conditions) and can be predicted analytically by surface minimization.
This result is very general and is shown to hold true for several well
known semi-classical models of nuclear interaction and even for a simple
Lennard-Jones potential. Also, in the limit of very large systems, when
?small size? effects can be neglected, those equilibrium configurations
seem to be restricted to a few structures reminiscent to the ?Pasta
Phases? expected in Neutron Star matter, but arising from a completely
different origin: In Neutron Star matter, the non-homogeneous structures
arise from a competition between nuclear and Coulomb interactions while
for ideal nuclear matter they emerge from finite (yet not ?small?) size
effects. The role of periodic boundary conditions and finite size
effects in Neutron Star matter simulations are reexamined.