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[ITensors] [ENHANCMENT] Non-Hermitian
dmrg (#913)
* nonHermitician * nonHermitician * nonHermitician * nonHermitician * Change DMRGObserver to allow complex energies * Change DMRGObserver to allow complex energies * Formatting and cleanup of tests * Replace complex_energy with energy_type * Redesign of DMRGObserver constructors Co-authored-by: leachinellato <leachinellato@outlook.com.ar> Co-authored-by: Miles <miles.stoudenmire@gmail.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,68 @@ | ||
| ######### | ||
| ## XXZ model with imaginary part | ||
| ######### | ||
| using ITensors | ||
|
|
||
| function Hamiltonian(sites, Δ::Float64, J::Float64, γ::Float64, h::Float64) | ||
| N = length(sites) | ||
| ampo = AutoMPO() | ||
|
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||
| for j in 1:(N - 1) | ||
| ampo += Δ, "Sz", j, "Sz", j + 1 | ||
| ampo += -(J + im * γ * (-1.0)^j), "Sx", j, "Sx", j + 1 | ||
| ampo += -(J + im * γ * (-1.0)^j), "Sy", j, "Sy", j + 1 | ||
| end | ||
| for j in 1:N | ||
| ampo += h * (-1.0)^j, "Sz", j | ||
| end | ||
| # Convert these terms to an MPO tensor network | ||
| return MPO(ampo, sites) | ||
| end | ||
|
|
||
| let | ||
| #model parameters | ||
| N = 4 | ||
| Δ = -0.70 | ||
| J = 1.0 | ||
| γ = 0.1 | ||
| h = 0.1 | ||
|
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| alg = "qr_iteration" | ||
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| #dmrg parameters | ||
| sweeps = Sweeps(1000) | ||
| minsweeps = 5 | ||
| maxdim!(sweeps, 50, 100, 200) | ||
| #cutoff!(sweeps, 1E-12) | ||
| etol = 1E-12 | ||
|
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| sites = siteinds("S=1/2", N; conserve_qns=false) | ||
|
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| #initial state | ||
| state = ["Emp" for n in 1:N] | ||
| p = N | ||
| for i in N:-1:1 | ||
| if p > i | ||
| #println("Doubly occupying site $i") | ||
| state[i] = "UpDn" | ||
| p -= 2 | ||
| elseif p > 0 | ||
| #println("Singly occupying site $i") | ||
| state[i] = (isodd(i) ? "Up" : "Dn") | ||
| p -= 1 | ||
| end | ||
| end | ||
| psi0 = randomMPS(sites, state) | ||
| @show flux(psi0) | ||
|
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| H = Hamiltonian(sites, Δ, J, γ, h) | ||
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| obs = DMRGObserver( | ||
| ["Sz"], sites; energy_tol=etol, minsweeps=minsweeps, complex_energies=true | ||
| ) | ||
|
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| energy, psi = dmrg( | ||
| H, psi0, sweeps; svd_alg=alg, observer=obs, outputlevel=1, ishermitian=false | ||
| ) | ||
| println("Final energy = $energy") | ||
| end |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,68 @@ | ||
| using ITensors | ||
|
|
||
| function Hamiltonian(sites, λ::Float64, k::Float64) | ||
| N = length(sites) | ||
| ampo = AutoMPO() | ||
|
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||
| for j in 1:(N - 1) | ||
| ampo += -0.5 * 2 * λ, "Sz", j, "Sz", j + 1 | ||
| end | ||
| for j in 1:N | ||
| ampo += -0.5 * 2 * im * k, "Sz", j | ||
| ampo += -0.5, "S+", j | ||
| ampo += -0.5, "S-", j | ||
| end | ||
| # Convert these terms to an MPO tensor network | ||
| return MPO(ampo, sites) | ||
| end | ||
|
|
||
| let | ||
| #----------------------------------------------------------------------- | ||
|
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| #models parameters | ||
| N = 4 | ||
| λ = 0.1 | ||
| k = 0.5 | ||
|
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| alg = "qr_iteration" | ||
|
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| #dmrg parameters | ||
| sweeps = Sweeps(1000) | ||
| minsweeps = 5 | ||
| maxdim!(sweeps, 50, 100, 200) | ||
| #cutoff!(sweeps, 1E-12) | ||
| etol = 1E-12 | ||
|
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| #----------------------------------------------------------------------- | ||
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| sites = siteinds("S=1/2", N; conserve_qns=false) | ||
| #----------------------------------------------------------------------- | ||
|
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| #inicial state | ||
| state = ["Emp" for n in 1:N] | ||
| p = N | ||
| for i in N:-1:1 | ||
| if p > i | ||
| state[i] = "UpDn" | ||
| p -= 2 | ||
| elseif p > 0 | ||
| state[i] = (isodd(i) ? "Up" : "Dn") | ||
| p -= 1 | ||
| end | ||
| end | ||
| psi0 = randomMPS(sites, state) | ||
| @show flux(psi0) | ||
| #----------------------------------------------------------------------- | ||
|
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| #----------------------------------------------------------------------- | ||
|
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| H = Hamiltonian(sites, λ, k) | ||
| #----------------------------------------------------------------------- | ||
|
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| obs = DMRGObserver(; energy_tol=etol, minsweeps=2, complex_energies=true) | ||
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| energy, psi = dmrg( | ||
| H, psi0, sweeps; svd_alg=alg, observer=obs, outputlevel=1, ishermitian=false | ||
| ) | ||
| println("Final energy = $energy") | ||
| end |