590 research outputs found
Complex free energy landscapes in biaxial nematics and role of repulsive interactions : A Wang - Landau study
General quadratic Hamiltonian models, describing interaction between crystal
molecules (typically with symmetry) take into account couplings
between their uniaxial and biaxial tensors. While the attractive contributions
arising from interactions between similar tensors of the participating
molecules provide for eventual condensation of the respective orders at
suitably low temperatures, the role of cross-coupling between unlike tensors is
not fully appreciated. Our recent study with an advanced Monte Carlo technique
(entropic sampling) showed clearly the increasing relevance of this cross term
in determining the phase diagram, contravening in some regions of model
parameter space, the predictions of mean field theory and standard Monte Carlo
simulation results. In this context, we investigated the phase diagrams and the
nature of the phases therein, on two trajectories in the parameter space: one
is a line in the interior region of biaxial stability believed to be
representative of the real systems, and the second is the extensively
investigated parabolic path resulting from the London dispersion approximation.
In both the cases, we find the destabilizing effect of increased cross-coupling
interactions, which invariably result in the formation of local biaxial
organizations inhomogeneously distributed. This manifests as a small, but
unmistakable, contribution of biaxial order in the uniaxial phase.The free
energy profiles computed in the present study as a function of the two dominant
order parameters indicate complex landscapes, reflecting the difficulties in
the ready realization of the biaxial phase in the laboratory.Comment: 23 pages, 12 figure
Relativistic and correlation effects in atoms
This review article deals with some case studies of relativistic and
correlation effects in atomic systems. After a brief introduction to
relativistic many-electron theory, a number of applications ranging from
correlation energy to parity non-conservation in atoms are considered. There is
a special emphasis on relativistic coupled-cluster theory as most of the
results presented here are based on it.Comment: Review article, 4 eps figures, latex 2
Probing CP violation with the electric dipole moment of atomic mercury
The electric dipole moment of atomic Hg induced by the nuclear Schiff
moment and tensor-pseudotensor electron-nucleus interactions has been
calculated. For this, we have developed and employed a novel method based on
the relativistic coupled-cluster theory. The results of our theoretical
calculations combined with the latest experimental result of Hg
electric dipole moment, provide new bounds on the T reversal or CP violation
parameters , the tensor-pseudotensor coupling constant
and . This is the most accurate
calculation of these parameters to date. We highlight the the crucial role of
electron correlation effects in their interplay with the P,T violating
interactions. Our results demonstrate substantial changes in the results of
earlier calculations of these parameters which can be attributed to the more
accurate inclusion of important correlation effects in the present work.Comment: 4 pages and 1 figur
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