141 research outputs found
Vibron Self--trapped States in Biological Macromolecules: Comparison of Different Theoretical Approaches
A study of the applicability of the variational treatments based on using of
the modified Lang-Firsov unitary transformation (MLF method) in the
investigation of the vibron self-trapped states in biological macromolecular
chains are presented. We compare the values of the ground state energy
predicted by MLF methods with the values of the ground state energy predicted
by the standard small-polaron theory, for various values of the basic energy
parameters of the system. We obtain regions in system parameter space where MLF
approach gives better description of the vibron states.Comment: 8 pages, 4 figures, To appear in the Proceedings of Conference
Dubna-Nano2012 (July 9 - 14, 2012
Vibron transport in macromolecular chains
We study the hopping mechanism of the vibron excitation transport in the
simple 1D model of biological macromolecular chains. We supposed that the
vibron interaction with thermal oscillations of the macromolecular structural
elements will result in vibron self -trapping, and the formation of the partial
dressed vibron state. With use of the modified Holstein polaron model, we
calculate vibron diffusivity in dependence of the basic system parameters and
temperature. We obtain that the vibron diffusivity smoothly decreases in non
adiabatic limit when the strength of the vibron-phonon coupling grows. However
this dependence becomes by discontinuous one in case of growth of the
adiabaticity of the system. The value of the critical point depends of the
system temperature, and at room temperatures it belongs to the low or
intermediate coupling regime. We discuss an application of these results to
study of vibron transport to 3D bundles of such macromolecules chains
considering it as polymer nanorods and to 2D polymer films organized from such
macromolecules.Comment: 4 pages, 6 figures, contribution to the Proceedings of the Conference
"Physical mesomechanics of multi-level systems`2014", September 3-5 2014,
Tomsk, Russi
On the influence of the "donor"/"acceptor" presence on the excitation states in molecular chains: non-adiabatic polaron approach
In the paper, we considered a molecular structure that consists of a
molecular chain and an additional molecule ("donor"/"acceptor") that can inject
(or remove) single excitation (vibron, electron, e.t.c.) onto the molecular
chain. We assumed that the excitation forms a self-trapped state due to the
interaction with mechanical oscillations of chain structure elements. We
analyzed the energy spectra of the excitation and showed that its state (when
it migrates to the molecular chain) has the properties of the non-adiabatic
polaron state. The conditions under which the excitation can migrate from one
subsystem to another were considered. It was shown that the presence of a
"donor" molecule cannot significantly change the properties of the excitation
located on the molecular chain. At the same time, the molecular chain can
affect the position of the energy level of the excitation localized on the
"donor" subsystem. Indirectly, this can influence the process of excitation
migration from one subsystem to another one. The influence of basic energy
parameters of the system and the environment temperature on this process are
discussed. The entire system was assumed to be in thermal equilibrium with the
environment
Electromagnetic pulse transparency in coupled cavity arrays through dispersion management
We theoretically demonstrated the possible emergence of slow-light
self-induced transparency solitons in the infinite one-dimensional coupled
cavity array, with each cavity containing a single qubit. We have predicted a
substantial dependence of pulse transparency on its dimensionless width
. In particular, short pulses whose widths range from to
exhibit simple, almost linear dispersion law with a finite
frequency gap of the order of the cavity array photonic band gap. That is, the
medium is opaque for very short pulses with carrier wave frequency below the
photonic gap. When the pulse width exceeds the critical one, a twin
transparency window separated by a finite band gap appears in the soliton pulse
dispersion law. Observation of predicted effects within the proposed setup
would be of interest for understanding the properties of self-induced
transparency effect in general and future applications in the design of quantum
technological devices
From Davydov solitons to decoherence-free subspaces: self-consistent propagation of coherent-product states
The self-consistent propagation of generalized [coherent-product]
states and of a class of gaussian density matrix generalizations is examined,
at both zero and finite-temperature, for arbitrary interactions between the
localized lattice (electronic or vibronic) excitations and the phonon modes. It
is shown that in all legitimate cases, the evolution of states reduces
to the disentangled evolution of the component states. The
self-consistency conditions for the latter amount to conditions for
decoherence-free propagation, which complement the Davydov soliton
equations in such a way as to lift the nonlinearity of the evolution for the
on-site degrees of freedom. Although it cannot support Davydov solitons, the
coherent-product ansatz does provide a wide class of exact density-matrix
solutions for the joint evolution of the lattice and phonon bath in compatible
systems. Included are solutions for initial states given as a product of a
[largely arbitrary] lattice state and a thermal equilibrium state of the
phonons. It is also shown that external pumping can produce self-consistent
Frohlich-like effects. A few sample cases of coherent, albeit not solitonic,
propagation are briefly discussed.Comment: revtex3, latex2e; 22 pages, no figs.; to appear in Phys.Rev.E
(Nov.2001
Two-vibron bound states in alpha-helix proteins : the interplay between the intramolecular anharmonicity and the strong vibron-phonon coupling
The influence of the intramolecular anharmonicity and the strong
vibron-phonon coupling on the two-vibron dynamics in an -helix protein
is studied within a modified Davydov model. The intramolecular anharmonicity of
each amide-I vibration is considered and the vibron dynamics is described
according to the small polaron approach. A unitary transformation is performed
to remove the intramolecular anharmonicity and a modified Lang-Firsov
transformation is applied to renormalize the vibron-phonon interaction. Then, a
mean field procedure is realized to obtain the dressed anharmonic vibron
Hamiltonian. It is shown that the anharmonicity modifies the vibron-phonon
interaction which results in an enhancement of the dressing effect. In
addition, both the anharmonicity and the dressing favor the occurrence of two
different bound states which the properties strongly depend on the interplay
between the anharmonicity and the dressing. Such a dependence was summarized in
a phase diagram which characterizes the number and the nature of the bound
states as a function of the relevant parameters of the problem. For a
significant anharmonicity, the low frequency bound states describe two vibrons
trapped onto the same amide-I vibration whereas the high frequency bound states
refer to the trapping of the two vibrons onto nearest neighbor amide-I
vibrations.Comment: may 2003 submitted to Phys. Rev.
Continuum Surface Energy from a Lattice Model
We investigate connections between the continuum and atomistic descriptions
of deformable crystals, using certain interesting results from number theory.
The energy of a deformed crystal is calculated in the context of a lattice
model with general binary interactions in two dimensions. A new bond counting
approach is used, which reduces the problem to the lattice point problem of
number theory. The main contribution is an explicit formula for the surface
energy density as a function of the deformation gradient and boundary normal.
The result is valid for a large class of domains, including faceted (polygonal)
shapes and regions with piecewise smooth boundaries.Comment: V. 1: 10 pages, no fig's. V 2: 23 pages, no figures. Misprints
corrected. Section 3 added, (new results). Intro expanded, refs added.V 3: 26
pages. Abstract changed. Section 2 split into 2. Section (4) added material.
V 4, 28 pages, Intro rewritten. Changes in Sec.5 (presentation only). Refs
added.V 5,intro changed V.6 address reviewer's comment
- …