1,701 research outputs found
Dynamical Mean Field Theory with the Density Matrix Renormalization Group
A new numerical method for the solution of the Dynamical Mean Field Theory's
self-consistent equations is introduced. The method uses the Density Matrix
Renormalization Group technique to solve the associated impurity problem. The
new algorithm makes no a priori approximations and is only limited by the
number of sites that can be considered. We obtain accurate estimates of the
critical values of the metal-insulator transitions and provide evidence of
substructure in the Hubbard bands of the correlated metal. With this algorithm,
more complex models having a larger number of degrees of freedom can be
considered and finite-size effects can be minimized.Comment: 5 pages, 4 figure
Generating Diophantine Sets by Virus Machines
Virus Machines are a computational paradigm inspired by
the manner in which viruses replicate and transmit from one host cell to
another. This paradigm provides non-deterministic sequential devices.
Non-restricted virus machines are unbounded virus machines, in the
sense that no restriction on the number of hosts, the number of instructions
and the number of viruses contained in any host along any computation
is placed on them. The computational completeness of these
machines has been obtained by simulating register machines. In this
paper, virus machines as set generating devices are considered. Then,
the universality of non-restricted virus machines is proved by showing
that they can compute all diophantine sets, which the MRDP theorem
proves that coincide with the recursively enumerable sets.Ministerio de EconomÃa y Competitividad TIN2012- 3743
The Mott transition in V_2 O_3 and Ni Se_x S_{2-x}: insights from dynamical mean field theory
We discuss some aspects of the pressure (or interaction) driven Mott
transition, in three dimensional transition metal oxides by means of dynami cal
mean field theory. We isolate the universal properties of the transition from
the aspects which depend more on the detailed chemistry of the compounds. In
this light we can understand the main differences and the remarkable
similarities between these systems. Both theory and experiment converge on the
transfer of spectral weight from low energies to high energies as the universal
mechanism underlying the Mott transition, and we comment on the possible
relevance of these ideas to other metal to non metal transitions.Comment: Talk presented at SCES 9
Equational reasoning with context-free families of string diagrams
String diagrams provide an intuitive language for expressing networks of
interacting processes graphically. A discrete representation of string
diagrams, called string graphs, allows for mechanised equational reasoning by
double-pushout rewriting. However, one often wishes to express not just single
equations, but entire families of equations between diagrams of arbitrary size.
To do this we define a class of context-free grammars, called B-ESG grammars,
that are suitable for defining entire families of string graphs, and crucially,
of string graph rewrite rules. We show that the language-membership and
match-enumeration problems are decidable for these grammars, and hence that
there is an algorithm for rewriting string graphs according to B-ESG rewrite
patterns. We also show that it is possible to reason at the level of grammars
by providing a simple method for transforming a grammar by string graph
rewriting, and showing admissibility of the induced B-ESG rewrite pattern.Comment: International Conference on Graph Transformation, ICGT 2015. The
final publication is available at Springer via
http://dx.doi.org/10.1007/978-3-319-21145-9_
Metal-Insulator transitions in the periodic Anderson model
We solve the Periodic Anderson model in the Mott-Hubbard regime, using
Dynamical Mean Field Theory. Upon electron doping of the Mott insulator, a
metal-insulator transition occurs which is qualitatively similar to that of the
single band Hubbard model, namely with a divergent effective mass and a first
order character at finite temperatures. Surprisingly, upon hole doping, the
metal-insulator transition is not first order and does not show a divergent
mass. Thus, the transition scenario of the single band Hubbard model is not
generic for the Periodic Anderson model, even in the Mott-Hubbard regime.Comment: 5 pages, 4 figure
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