Software

We aim to make as much of the software we write as possible both open-source and easily accessible. Below, one can find github repositories associated with different projects that are either underway, or have been published. If the desired code can't be found, feel free to contact us.
FermiCG

FermiCG ("Fermionic Course-Graining") is a code for computing high-accuracy electronic states for molecular systems in a tensor product state (TPS) basis. Unlike in the traditional Slater determinant basis, a TPS basis can be chosen such that each basis vector has a considerable amount of electron correlation already included. As a result, the exact wavefunction in this basis can be considerably more compact. This increased compactness comes at the cost of a significant increase in complexity for determining matrix elements. So far, we have implemented multiple approach for discovering highly accurate wavefunctions in this TPS basis. This package includes: The repository found contains the code used to generate the results for publications:

  • Generalization of the tensor product selected CI method for molecular excited states
    Nicole M. Braunscheidel, Vibin Abraham, Nicholas J. Mayhall
    Preprint, (2023): preprint

  • Coupled electron pair-type approximations for tensor product state wavefunctions
    Vibin Abraham and Nicholas J. Mayhall
    Journal of Chemical Theory and Computation 18, 4856 (2022): article | preprint

  • Selected Configuration Interaction in a Basis of Cluster State Tensor Products
    Vibin Abraham and Nicholas J. Mayhall
    Journal of Chemical Theory and Computation, 16, 6098-6113 (2020): article | preprint

ADAPT-VQE

This code uses uses PySCF for molecular integrals and OpenFermion for forming the fermion-qubit mapping. This is a noise free implementation which uses direct exponentiation of Pauli operators in the full Hilbert space. As such, the code is limited to about 6 spatial orbitals. For product form ansatze, an efficient recursive gradient algorithm is used for faster quasi-Newton optimization. The repository found contains the code used to generate the results for publications:

  • An adaptive variational algorithm for exact molecular simulations on a quantum computer
    Harper R. Grimsley, Sophia E. Economou, Edwin Barnes, N. J. Mayhall
    Nature Communications, 10, 3007, (2019): article | preprint

CtrlQ

CtrlQ is an open-source tool designed to simulate a gate-free state preparation on a Transmon qubit device using analog control pulses. The analog control pulses can be variationally shaped to drive an initial state to a target state in the framework of ctrl-VQE. In molecular systems, ctrl-VQE can be used to drive the initial Hartree Fock state to the full configuration interaction (FCI) state with substantial pulse duration speedups as compared to a gate-based compilation. The control quantum program (CtrlQ) is written in python with bindings to C++ codes for highly efficient time-evolution of quantum systems either using an ordinary-differential-equation or the Suzuki-Trotter expansion. The repository found contains the code used to generate the results for publications:

  • Gate-free state preparation for fast variational quantum eigensolver simulations: ctrl-VQE
    Oinam Romesh Meitei*, Bryan T. Gard*, George S. Barron, David P. Pappas, Sophia E. Economou, Edwin Barnes, Nicholas J. Mayhall
    Submitted, (2020): preprint *Co-first authors

Fock Space CI (DETCI)

This code uses presents and interface to use the RAS-CI functionality of the DETCI module in PSI4 to create the target configuration spaces for the various Fock-CI methods. As a string-based implementation, this code is general for arbitrary numbers of spin-flips/IPs/EAs, but comes at the cost of a larger computational overhead, including string based indexing, and full two-electron integral storage. This repository contains the code used to generate the results for publications:

  • A Combined Spin-Flip and IP/EA Approach for Handling Spin and Spatial Degeneracies: Application to Double Exchange Systems
    Shannon E. Houck, N. J. Mayhall
    Journal of Chemical Theory and Computation, 15, 2278-2290 (2019): article | preprint

n-body Tucker

This code implements the n-body Tucker approach for isotropic Heisenberg spin Hamiltonians. The repository found contains the code used to generate the results for publications:

  • Using higher-order singular value decomposition to define weakly coupled and strongly correlated cluster states: the n-body Tucker approximation
    N. J. Mayhall
    Journal of Chemical Theory and Computation, 13, 4818-4828, (2017): article

PsiEmbed

This code implements the interface to both PSI4 and PySCF for performing WFT-in-DFT projection based embedding methods described in the following publications:

  • Simple and efficient truncation of virtual spaces in embedded wave functions via concentric localization
    Daniel Claudino, N. J. Mayhall
    Journal of Chemical Theory and Computation, 15, 6085-6096 (2019): article | preprint

  • Automatic Partition of Orbital Spaces Based on Singular Value Decomposition in the Context of Embedding Theories
    Daniel Claudino, N. J. Mayhall
    Journal of Chemical Theory and Computation, 15, 1053-1064 (2019): article | preprint