Choosing a DFT Engine

SPARC supports six DFT engines. Set dft_calculator.engine in input.yaml to select one. See DFT Calculator for the full API reference.

VASP

Best for periodic solids and surfaces. Requires a commercial VASP licence.

Requirements:

VASP binary (vasp_std, vasp_gam, etc.)
POTCAR files — set export VASP_PP_PATH=/path/to/potcar_files

Template file: INCAR

dft_calculator:
  engine: "VASP"
  template_file: "INCAR"
  exe_command: "mpirun -np 16 vasp_std"

CP2K

Open-source alternative for periodic systems (solids, surfaces, liquids).

Requirements:

CP2K binary + basis-set/pseudopotential library
cp2k_template.inp in the project root

dft_calculator:
  engine: "CP2K"
  template_file: "cp2k_template.inp"

ORCA

Suitable for molecular systems requiring high-level correlated methods (e.g., CCSD(T), hybrid DFT). Non-periodic; SPARC automatically removes periodic boundary conditions from the structure.

dft_calculator:
  engine: "ORCA"
  template_file: "orca_template.inp"
  exe_command: "/path/to/orca"

xTB

Semi-empirical tight-binding (GFN1-xTB, GFN2-xTB). Very fast — useful for large molecules or rapid screening before committing to DFT.

Warning

xTB is a non-periodic calculator. Periodic boundary conditions are automatically removed from the structure at runtime. As a result, the NPT ensemble is not supported with xTB — the barostat requires a periodic cell to compute stress and apply volume coupling. Use NVE or NVT instead. SPARC will raise an error if NPT is requested with xTB.

dft_calculator:
  engine: "xTB"
  template_file: "xtb_template.inp"

Quantum ESPRESSO (QE)

Open-source plane-wave DFT for periodic systems. k-points default to Gamma-only sampling; override by specifying kpts in the template.

dft_calculator:
  engine: "QE"
  template_file: "qe_template.in"
  exe_command: "mpirun -np 4 pw.x"

Gaussian

For molecular (non-periodic) systems. Periodicity is auto-removed. Uses a key = value template file.

dft_calculator:
  engine: "Gaussian"
  template_file: "gaussian_template.inp"
  exe_command: "g16"