Improved contraction of finite projected entangled pair states

We present an improved version of the algorithm contracting and optimizing finite projected entangled pair states (fPEPS) in conjunction with projected entangled pair operators (PEPOs). Our work has two components to it. First, we explain in detail the characteristic contraction patterns that occur in fPEPS calculations and how to slice them such that peak memory occupation remains minimal while ensuring efficient parallel computation. Second, we combine controlled bond expansion [A. Gleis, J.-W. Li, and J. von Delft, ] with randomized singular value decomposition [V. Rokhlin, A. Szlam, and M. Tygert, ] and apply it throughout the fPEPS algorithm. We present benchmark results for the Hubbard model for system sizes up to <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mn>8</a:mn> <a:mo>×</a:mo> <a:mn>8</a:mn> </a:mrow> </a:math> and SU(2) symmetric bond dimension of up to <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mi>D</b:mi> <b:mo>=</b:mo> <b:mn>6</b:mn> </b:mrow> </b:math> for PEPS bonds and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mi>χ</c:mi> <c:mo>=</c:mo> <c:mn>500</c:mn> </c:mrow> </c:math> for the environment bonds. Finally, we comment on the state and future of the fPEPS-PEPO framework.