First Calculations

The examples below run one molecular and one periodic CIDER calculation. The complete PySCF and GPAW guides cover numerical choices, properties, and restarts.

Molecule with PySCF

The packaged CIDER26XC molecular model uses the normal PySCF molecular and SCF objects:

#!/usr/bin/env python
"""Closed-shell molecular CIDER26XC calculation in PySCF."""

import argparse

from pyscf import dft, gto

from ciderpress.pyscf.dft import make_cider_calc

MODELS = ("CIDER26XCCHEM", "CIDER26XCCHEMD4", "CIDER26XCSURFSCI")


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--model", choices=MODELS, default="CIDER26XCCHEM")
    args = parser.parse_args()

    mol = gto.M(
        atom="""
        O  0.000000  0.000000  0.117790
        H  0.000000  0.755453 -0.471161
        H  0.000000 -0.755453 -0.471161
        """,
        basis="def2-tzvp",
        charge=0,
        spin=0,
    )

    base = dft.RKS(mol)
    base.grids.level = 3
    mf = make_cider_calc(base, args.model)
    mf = mf.density_fit(auxbasis="def2-universal-jfit")
    mf.conv_tol = 1e-9
    mf.max_cycle = 200
    energy = mf.kernel()

    if not mf.converged:
        raise RuntimeError("CIDER SCF did not converge")

    print(f"model = {args.model}")
    print(f"total energy = {energy:.12f} Ha")
    if hasattr(mf, "e_vdw_expected"):
        print(f"SCF/base energy = {mf.e_tot_base:.12f} Ha")
        print(f"expected dispersion = {mf.e_vdw_expected:.12f} Ha")
        print(f"dispersion adjustment = {mf.e_vdw_delta:.12f} Ha")


if __name__ == "__main__":
    main()

Run it from the repository root with:

python examples/pyscf/production_calc.py --model CIDER26XCCHEM

The example raises RuntimeError when the SCF does not converge. It prints the base, expected dispersion, and adjustment terms for every CIDER26XC model. With CIDER26XCCHEMD4 they show how the final total was assembled; CIDER26XCCHEM and CIDER26XCSURFSCI print zero for the dispersion entries.

Exchange-only model with PySCF

Packaged CIDER23X and CIDER24X are exchange functionals. The following example supplies the PBE0/CIDER surrogate composition:

#!/usr/bin/env python
"""Run a packaged CIDER23X or CIDER24X exchange model with PySCF."""

import argparse

from pyscf import dft, gto

from ciderpress.dft.model_utils import CIDER23X_MODELS, CIDER24X_MODELS
from ciderpress.pyscf.dft import make_cider_calc

MODELS = CIDER23X_MODELS + CIDER24X_MODELS


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--model", choices=MODELS, default="CIDER23X_NL_MGGA_DTR")
    args = parser.parse_args()

    mol = gto.M(
        atom="H 0 0 0; H 0 0 0.74",
        basis="def2-svp",
        charge=0,
        spin=0,
    )

    base = dft.RKS(mol)
    base.grids.level = 3
    mf = make_cider_calc(
        base,
        args.model,
        xmix=0.25,
        xkernel="GGA_X_PBE",
        ckernel="GGA_C_PBE",
    )
    mf = mf.density_fit(auxbasis="def2-universal-jfit")
    mf.conv_tol = 1e-9
    mf.max_cycle = 200
    energy = mf.kernel()

    if not mf.converged:
        raise RuntimeError("CIDER SCF did not converge")
    print(f"model = {args.model}")
    print(f"total energy = {energy:.12f} Ha")


if __name__ == "__main__":
    main()

The explicit xmix, xkernel, and ckernel arguments define the surrogate-hybrid composition. For CIDER24X, install ciderpress[cider24] and select the corresponding name.

Periodic solid with GPAW

The periodic example first writes a full PBE checkpoint and then restarts it with CIDER26XCSURFSCI:

#!/usr/bin/env python
"""PBE-seeded periodic CIDER26XCSURFSCI calculation in classic GPAW."""

from ase.build import bulk
from ase.parallel import parprint
from gpaw import GPAW, PW, Mixer

from ciderpress.gpaw.calculator import CiderGPAW, get_cider_functional


def main():
    atoms = bulk("Si")
    atoms.calc = GPAW(
        xc="PBE",
        mode=PW(400),
        kpts={"size": (4, 4, 4), "gamma": False},
        occupations={"name": "fermi-dirac", "width": 0.1},
        mixer=Mixer(0.05, 5, 50),
        convergence={
            "energy": 1e-5,
            "density": 1e-5,
            "eigenstates": 1e-3,
            "bands": "occupied",
        },
        parallel={"augment_grids": True},
        txt="si_pbe.txt",
    )
    atoms.get_potential_energy()
    # The production models are meta-GGAs and need the wavefunctions to
    # reconstruct the kinetic-energy density after restart.
    atoms.calc.write("si_pbe.gpw", mode="all")

    xc = get_cider_functional(
        "CIDER26XCSURFSCI",
        xmix=1.0,
        xkernel=None,
        ckernel=None,
        pasdw_store_funcs=False,
    )
    calc = CiderGPAW(
        restart="si_pbe.gpw",
        xc=xc,
        mixer=Mixer(0.05, 5, 50),
        occupations={"name": "fermi-dirac", "width": 0.1},
        maxiter=500,
        parallel={"augment_grids": True},
        txt="si_cider.txt",
    )
    atoms = calc.get_atoms()
    atoms.calc = calc
    energy = atoms.get_potential_energy()
    calc.write("si_cider.gpw", mode="all")
    parprint(f"CIDER26XCSURFSCI energy = {energy:.12f} eV")


if __name__ == "__main__":
    main()

Run GPAW examples with the MPI launcher and rank count appropriate for the installed GPAW build, for example:

mpirun -np 4 python examples/gpaw/production_calc.py

Continue with Molecular Calculations with PySCF or Periodic and Isolated Calculations with GPAW; Handling SCF Convergence Issues gives concrete restart settings for difficult SCF calculations.