Basic Usage

There are only three steps to run BE calculations using QuEmb:

  1. Define fragments using fragpart.

  2. Initialize BE using BE.

  3. Density matching or chemical potential optimization using BE.optimize

QuEmb requires molecular & Hartree-Fock calculation objects from pyscf. Refer to pyscf documentations: Molecules: 1 & 2, Solids: 3 & 4

Simple example of BE calculation on molecular system:

from molbe import fragpart, BE

# Perform pyscf calculations to get mol, mf objects
# See quemb/example/molbe_h8_density_matching.py
# get mol: pyscf.gto.M
# get mf: pyscf.scf.RHF

# Define fragments
myFrag = fragpart(be_type='be2', mol=mol)

# Initialize BE
mybe = BE(mf, myFrag)

# Perform density matching in BE
mybe.optimize(solver='CCSD')

Simple example of periodic BE calculation on 1D periodic system:

from kbe import fragpart, BE

# Perform pyscf pbc calculations to get cell, kmf, kpts
# See quemb/example/kbe_polyacetylene.py
# get cell: pyscf.pbc.gto.Cell
# get kmf: pyscf.pbc.scf.KRHF
# get kpts: 2D array of k-points

nk = 3 # no. of kpoints
# Define fragments
myFrag = fragpart(be_type='be2', mol=cell, kpt=[1,1,nk])

# Initialize BE
mybe = BE(mf, myFrag, kpts=kpts)

# Perform density matching in BE
mybe.optimize(solver='CCSD')