PySEQM — reference equations for the s/p two-center kernels
===========================================================

The closed-form s/p two-center two-electron integrals, the electron-core
attraction terms, and the diatomic rotation to the local frame implemented in
src/integrals.rs and src/overlap.rs follow the reference equations of:

  PySEQM (PYthon Semi-Empirical Quantum Mechanics)
  https://github.com/lanl/PYSEQM

  G. Zhou, B. Nebgen, N. Lubbers, W. Malone, A. M. N. Niklasson, S. Tretiak,
  "Graphics Processing Unit-Accelerated Semiempirical Born Oppenheimer
   Molecular Dynamics Using PyTorch",
  J. Chem. Theory Comput. 16, 4951-4962 (2020).

PySEQM is distributed under the BSD 3-Clause License. No PySEQM source code is
redistributed in this repository; the Rust implementation is original code that
reproduces the same published NDDO working equations.

ACTION REQUIRED BEFORE REDISTRIBUTION: if any PySEQM source is ever vendored
into this repository, copy the verbatim LICENSE file (including its copyright
line) from the upstream repository above into third_party/pyseqm/LICENSE, as
BSD-3-Clause requires the copyright notice and license text to be retained.
