# 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

- “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. - “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. - “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.