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pDMET in PySCF

We develop the LASSCF, CAS-DMET, pDMET methods in PySCF as described below

pDMET

pdmet is a free and open-source Python3 program to perform density matrix embedding theory (DMET) calculation on periodic systems. Currently, pDMET is able to compute ground-state energy, local excitation energies as well as quasiparticle band structure using variety of quantum chemical solvers, such as: FCI, MP2, DMRG, SHCI, CCSD, CASSCF and NEVPT2. It is available athttps://github.com/mitra054/pDMET which is forked from https://github.com/hungpham2017/pDMET

Prerequisites

PySCF: a Python package for quantum chemistry calculations on molecules and solids (https://pyscf.org)
pyWannier90: a Python interface for wannier90 used to construct Maximally-localized Wannier functions available at https://github.com/hungpham2017/pyWannier90

Usage

The code can be used by importing the following modules

import pywannier90
from pdmet import dmet
pdmet = dmet.pDMET(cell, kmf, w90, solver = 'MP2')

where kmf is a standard PySCF periodic mean-field method instance, ‘w90’ is a converged Wannier90 object and MP2 is the high-level quantum chemistry solver used.

Here is how the dmet module can be used along with the SA-CASSCF high-level solver to find excitation energies

'''DMET calculation - SA-CASSCF'''
pdmet = dmet.pDMET(cell, kmf, w90, solver = 'SA-CASSCF') 
pdmet.impCluster = [3]                                   # specifies the atom/atoms considered in the "impurity space"
pdmet.twoS = 0                                           # specifies the spin of the system
pdmet.cas = (2,2)                                        # the active space using the notation: (elec,orb)
pdmet.molist = [1,3]                                     # using MOs 1 and 3 in the active space (starts from 0)  
pdmet.initialize()                                       # initializes the dmet calculation
pdmet.one_shot()                                         # performs a single-shot DMET

References

  1. “Can Density Matrix Embedding Theory with the Complete Activate Space Self-Consistent Field Solver Describe Single and Double Bond Breaking in Molecular Systems?,” H. Q. Pham, V Bernales, and L Gagliardi, [J. Chem. Theory Comput.](https://doi.org/10.1021/acs.jctc.7b01248 2018, 14, 1960.
  2. “Periodic Electronic Structure Calculations with the Density Matrix Embedding Theory,” H. Q. Pham, M. R. Hermes, L. Gagliardi, [J. Chem. Theory Comput.] (https://doi.org/10.1021/acs.jctc.9b00939) 2020, 16, 130.
  3. “Excited States of Crystalline Point Defects with Multireference Density Matrix Embedding Theory,” A. Mitra, H. Q. Pham, R Pandharkar, M R. Hermes, and L Gagliardi, [J. Phys. Chem. Lett.] (https://doi.org/10.1021/acs.jpclett.1c03229) 2021, 12, 11688.