ETN school 2023 - PEPS lectures and tutorial

(infinite) projected entagled-pair states and algorithms for European Tensor Network school 2023 (https://nextcloud.tfk.ph.tum.de/etn/index.php/schools/2023-school/)

Notes

• General introduction to iPEPS as a variational ansatz and application to J1-J2 model
• Introduction to CTMRG and application to classical 2D ferromagnetic Ising model at finite temperature

Tutorial

1. Classical 2D Ising model - contracting the partition function with CTMRG
2. Optimization of spin-1/2 2D antiferromagnetic Heisenberg model on a square lattice with single-site iPEPS

Using peps-torch:

3. Specific PEPS: S=2 AKLT state and spin-1/2 nearest-neighbour resonating valence bond state
4. Simple update for spin-1/2 2D antiferromagnetic Heisenberg model with 2x2 unit cell