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Fermonic PEPS using parity conserving tensors
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- bsarray and parray classes
- einsum
- create repo
- general parray and einsum
- initialization of peps,
in particular merge & transpose of parray
- operations: mps_dot & mpo_apply_to_mps
- peps_dot and peps contraction
- autograd optimization
- Hessenberg hamiltonian - fix bug for 3*3 case [fixed for Sp*Sm]
- autograd tested against finite difference
- save & load PEPS => callback
- SVD-mps/mpo compression for larger systems
- fix bugs in <A|H|B>
- Monte-Carlo - seems to be very suitable for long-range Hamiltoinan;
we only needs to read out the coefficients <n|PEPS> for given |n>.
Note: <n|H|PEPS> is required to avoid additional RI.
- fermionic operations
Starting from 2-by-2:
Q1: how operators are represented and act on PEPS ?
Q2: how <PEPS|H|PEPS> can be converted to bosonic TNS diagrams?
Q3: particle number projector? any advantage
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TODOs
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- memory issue? => larger systems
- optimize the contraction scheme for <PEPS|H|PEPS>;
reusing intermediates or using PEPO
- regularize the PEPS for better numerical stability!
divide each by max element
- eigenvalue optimization for small problem
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To run it:
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- Requirement: autograd
- Download and change name for directory from fPEPS to fpeps2017.
Go to fermions and run, e.g., peps2by2.py.