  Quantum computational chemistry (QCC) is the use of quantum computers to
solve problems in computational quantum chemistry. We develop a high
performance variational quantum eigensolver (VQE) simulator for simulating
quantum computational chemistry problems on a new Sunway supercomputer. The
major innovations include: (1) a Matrix Product State (MPS) based VQE simulator
to reduce the amount of memory needed and increase the simulation efficiency;
(2) a combination of the Density Matrix Embedding Theory with the MPS-based VQE
simulator to further extend the simulation range; (3) A three-level
parallelization scheme to scale up to 20 million cores; (4) Usage of the Julia
script language as the main programming language, which both makes the
programming easier and enables cutting edge performance as native C or Fortran;
(5) Study of real chemistry systems based on the VQE simulator, achieving
nearly linearly strong and weak scaling. Our simulation demonstrates the power
of VQE for large quantum chemistry systems, thus paves the way for large-scale
VQE experiments on near-term quantum computers.
