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