An efficient density matrix renormalization group (DMRG) algorithm is presented and applied to Y junctions, systems with three arms of n sites that meet at a central site. The accuracy is comparable to DMRG of chains. As in chains, new sites are always bonded to the most recently added sites and the superblock Hamiltonian contains only new or once renormalized operators. Junctions of up to N=3n+1≈500 sites are studied with antiferromagnetic (AF) Heisenberg exchange J between nearest-neighbor spins S or electron transfer t between nearest neighbors in half-filled Hubbard models. Exchange or electron transfer is exclusively between sites in two sublattices with NA≠NB. The ground state (GS) and spin densities ρr=⟨Szr⟩ at site r are quite different for junctions with S=1/2, 1, 3/2, and 2. The GS has finite total spin SG=2S(S) for even (odd) N and for MG=SG in the SG spin manifold, ρr>0(
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: M.K. thanks DST for support through Ramanujan Fellowship
No. SR/S2/RJN-69/2012 and DST for funding computation
facility through Grant No. SNB/MK/14-15/137. Z.G.S. thanks
NSF for partial support of this work through the Princeton
MRSEC (Grant No. DMR-0819860). S.R. thanks DST India
for financial support.