Learn to Use ITensor

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DMRG Interface

The density matrix renormalization group (DMRG) is a very powerful algorithm for optimizing matrix product states (MPS) for ground states and low-lying excited states of one-dimensional (and quasi-one-dimensional) Hamiltonians.

The ITensor DMRG code works with Hamiltonians in matrix product operator (MPO) form so that a single DMRG code can work for a very wide range of different Hamiltonians and local Hilbert spaces.

ITensor also offers DMRG routines for more general optimization tasks, including

Synopsis

int N = 100;
auto sites = SpinOne(N);

auto psi = MPS(sites);

auto ampo = AutoMPO(sites);
for(int j = 1; j < N; ++j)
    {
    ampo += "Sz",j,"Sz",j+1;
    ampo += 0.5,"S+",j,"S-",j+1;
    ampo += 0.5,"S-",j,"S+",j+1;
    }
auto H = MPO(ampo);

auto sweeps = Sweeps(5);
sweeps.maxm() = 10,40,100,200,200;
sweeps.cutoff() = 1E-8;

auto energy = dmrg(psi,H,sweeps,{"Quiet",true});
//                  ^ psi passed by reference,
//                    can measure properties afterwards

printfln("Ground state energy = %.20f",energy);

Basic DMRG interface

Generalized DMRG interfaces


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