979 research outputs found
A Variational Approach to Nonlocal Exciton-Phonon Coupling
In this paper we apply variational energy band theory to a form of the
Holstein Hamiltonian in which the influence of lattice vibrations (optical
phonons) on both local site energies (local coupling) and transfers of
electronic excitations between neighboring sites (nonlocal coupling) is taken
into account. A flexible spanning set of orthonormal eigenfunctions of the
joint exciton-phonon crystal momentum is used to arrive at a variational
estimate (bound) of the ground state energy for every value of the joint
crystal momentum, yielding a variational estimate of the lowest polaron energy
band across the entire Brillouin zone, as well as the complete set of polaron
Bloch functions associated with this band. The variation is implemented
numerically, avoiding restrictive assumptions that have limited the scope of
previous assaults on the same and similar problems. Polaron energy bands and
the structure of the associated Bloch states are studied at general points in
the three-dimensional parameter space of the model Hamiltonian (electronic
tunneling, local coupling, nonlocal coupling), though our principal emphasis
lay in under-studied area of nonlocal coupling and its interplay with
electronic tunneling; a phase diagram summarizing the latter is presented. The
common notion of a "self-trapping transition" is addressed and generalized.Comment: 33 pages, 11 figure
“Privilege” Factor in Economic Policy of Bolsheviks and Kronstadt Rebellion
The influence of the Kronstadt mutiny (March 1921) on the change in the economic course of the Bolsheviks is analyzed. The results of a comparative analysis of different conceptual approaches to its interpretation as a factor of influence are presented. The authors consider the food dictatorship to be the fundamental principle of war communism, periodically softened by campaigns to endow workers with “privileges” in the form of the right to transport food; contemporaries talked about “benefits”. An overview of events, which allows us to consider “privileges” as the main factor in the activation of illegal market relations in 1918—1921is provided in the article. Its novelty lies in the attribution of the Kronstadt mutiny as an essential reason for the transition of the Leninist leadership not to the NEP, but to the next “privileged” operation. At the same time, the authors of the article argue that the accumulation of concessions (“privileges”), accelerated by the rebellion, led in August 1921 to the legalization of freedom of trade and to the NEP. Great attention is paid to the issue of the social basis of the mutiny, since, among other things, the authors see the sources of fearlessness and despair of the insurgents in this circumstance. A. Davydov and V. Khutsieva prove that the rebels primarily acted on behalf of that part of the peasantry that managed to save their bread from the Bolshevik requisitions
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