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Basis & MO Generation

CHAMP requires a trial wavefunction consisting of a determinantal part (Orbitals) and a Jastrow factor.

The most robust way to generate input files is using the TREXIO format and the trex2champ converter.

  1. Generate TREXIO File:

    • Run a calculation in a supported code (Quantum Package, GAMESS, PySCF).
    • Export the result to a TREXIO file (e.g., molecule.hdf5).
    • See Using TREXIO Files for details.

  2. Convert to CHAMP Format:

    • Use the trex2champ tool to extract the necessary files. 
      trex2champ molecule.hdf5
    • This will generate:
      • molecule.xyz (Geometry)
      • <basis_name>.basis.<element> (Basis sets for each element)
      • orbitals.lcao (Molecular orbitals)
      • determinants.det (Determinants)
      • ecp.dat (Pseudopotentials, if applicable)

  3. Organize Files:

    • Move the generated files to a pool/ directory.
    • CHAMP looks for basis files in the pool/ directory by default.

Manual File Creation

If you are not using TREXIO, you must ensure your files follow the specific CHAMP formats.

Basis Sets

  • Format: Radial grid representation (not Gaussian exponents directly).
  • Naming: <basis_name>.basis.<element> (e.g., BFD.basis.C).
  • Location: Must be in the pool/ directory.
  • See Basis Sets for the file format specification.

Molecular Orbitals

  • Format: .lcao or .orb file containing LCAO coefficients.
  • Ordering: Atomic orbitals must follow the TREXIO alphabetical convention (e.g., X, Y, Z for p-orbitals).
  • Spin: For open-shell systems, you need separate files for alpha and beta orbitals.
  • See Molecular Orbitals for details.

Input Configuration

In your CHAMP input file:

%module general
    pool   './pool/'
    basis  'BFD'      # Prefix for basis files
%endmodule

load orbitals  $pool/orbitals.lcao