English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The density matrix renormalization group (DMRG) method introduced by Whitefor the study of strongly interacting electron systems is reviewed; the methodis variational and considers a system of localized electrons as the union oftwo adjacent fragments A, B. A density matrix rho is introduced, whoseeigenvectors corresponding to the largest eigenvalues are the most significant,the most probable states of A in the presence of B; these states are retained,while states corresponding to small eigenvalues of rho are neglected. It isconjectured that the decreasing behaviour of the eigenvalues is gaussian. TheDMRG method is tested on the Pariser-Parr-Pople Hamiltonian of a cyclic polyene(CH)_N up to N=34. A Hilbert space of dimension 5 x 10^+18 is explored. Theground state energy is 10^-3 eV within the full CI value in the case N=18. TheDMRG method compares favourably also with coupled cluster approximations. Theunrestricted Hartree-Fock solution (which presents spin density waves) isbriefly reviewed, and a comparison is made with the DMRG energy values.Finally, the spin-spin and density-density correlation functions are computed;the results suggest that the antiferromagnetic order of the exact solution doesnot extend up to large distances but exists locally. No charge density wavesare present.Comment: 8 pages, RevTex, 2 figures, to be published in the Journal of  Chemical Physic

The density matrix renormalization group method: Application to the PPP model of a cyclic polyene chain