Symmetry and Preprocessing - COMPASS Module
The COMPASS module primarily handles the initialization of computational tasks. This includes reading user-defined molecular structures, basis sets, and other fundamental information; determining molecular symmetry and point groups; generating symmetry-adapted orbitals; and converting this data into BDF’s internal storage format. Key parameters for the Compass module include:
Basis Parameter Type: String
Specifies the name of the basis set used for the calculation. BDF basis sets are stored in $BDFHOME/basis_library. The basis sets for all atoms in the current calculation must be placed in the file specified by this parameter. Since basis sets are read via this file, users can assign different basis sets to different atoms using custom basis set files (see Custom Basis Set instructions).
$Compass Basis cc-pVDZ Geometry H 0.00 0.00 0.707 H 0.00 0.00 -0.707 End Geometry $End
Basis-block Parameter Type: String
Allows specifying different basis sets for different elements. The first line is the default basis set. Subsequent lines assign other basis sets to specific elements or atoms using the format element=basisname or element1,element2, …,elementn=basisname. Must end with End Basis.
$Compass
Basis-block
3-21g
C,N = 6-31g
Xe = cc-pvdz-pp
End Basis
Geometry
H 0.0 0.0 -1.1
C 0.0 0.0 0.0
N 0.0 0.0 1.0
Xe 3.0 0.0 0.0
End geometry
$End
MPEC+COSX Parameter Type: Boolean
Specifies the use of the Multipole Expansion of Coulomb Potential (MPEC) method to calculate the J matrix and the Chain-of-Sphere Exchange (COSX) method to calculate the K matrix.
RI-J , RI-K , RI-C Parameter Type: String
Auxiliary basis sets for the Density-Fitting (DF) approximation acceleration algorithm.
RI-J: Coulomb fitting basis set
RI-K: Exchange fitting basis set
RI-C: Correlation fitting basis set
$Compass
Basis
DEF2-SVP
RI-J
DEF2-SVP
Geometry
H 0.00 0.00 0.707
H 0.00 0.00 -0.707
End Geometry
$End
Geometry Parameter Type: String Array
Specifies the molecular structure for the calculation. Can be in Cartesian coordinate mode or internal coordinate mode. Molecular coordinate definitions start on the line following the Geometry parameter and end on the line before End Geometry.
Cartesian Coordinates mode
$Compass
Basis
cc-pVDZ
Geometry
H 0.00 0.00 0.707
H 0.00 0.00 -0.707
End Geometry
$End
Internal Coordinates mode
$Compass
Basis
cc-pVDZ
Geometry
O
H 1 0.9
H 1 0.9 2 109.0
End Geometry
$End
Restart Parameter Type: Boolean
Uses coordinates from the $BDFTASK.optgeom file for the calculation instead of the coordinates given under the Geometry keyword, where $BDFTASK is the input filename without the .inp suffix. Note: Although the coordinate values under the Geometry keyword are not used in this case, they cannot be omitted. The atom types, number, and order must match exactly; only the coordinate values can be arbitrary. For example, if the input file is named 1.inp and the 1.optgeom file contains:
GEOM
O 0. 0. 0.
H 0. 0. 2.
H 0. 2. 0.
Then a $compass module like the following in 1.inp will run correctly:
$compass
...
geometry
O 0. 0. 0.
H 0. 0. 2.1
H 0.1 2.0 0.
end geometry
restart
...
$end
This input is equivalent to (even if units of Å were specified above):
$compass
...
geometry
O 0. 0. 0.
H 0. 0. 2.
H 0. 2. 0.
end geometry
unit
bohr
...
$end
However, the $compass module in 1.inp cannot be written like the following because the number of atoms doesn’t match the .optgeom file:
$compass
...
geometry
O 0. 0. 0.
H 0. 2.1 0.
end geometry
restart
...
$end
Nor can it be written like this, because the atom order doesn’t match the .optgeom file:
$compass
...
geometry
H 0. 2.1 0.
O 0. 0. 0.
H 0. 0. 2.1
end geometry
restart
...
$end
restart is primarily used for resuming interrupted geometry optimizations. Using the 1.inp example, if 1.inp is an input file for a geometry optimization that didn’t finish normally (e.g., due to non-convergence, an error, or user termination), the structure from the last optimization step is saved in 1.optgeom. Adding the restart keyword to the $compass module in 1.inp and rerunning 1.inp allows resuming the geometry optimization from the last structure, without manually copying the contents of 1.optgeom into 1.inp.
Group Parameter Type: String
Specifies the molecular symmetry point group. BDF automatically determines molecular symmetry. HF/DFT/TDDFT support high-order molecular point groups. However, some electron correlation methods like MCSCF and MRCI only support D2h and its subgroups. This parameter can be used to force BDF to use an Abelian group for such calculations.
# Benzene has highest symmetry D6h. Without specifying a group, BDF determines D6h symmetry. $COMPASS Title C6H6 Molecule test run, cc-pVDZ Basis cc-pVDZ Geometry C 0.00000000000000 1.39499100000000 0.00000000000000 C -1.20809764405066 0.69749550000000 0.00000000000000 C 0.00000000000000 -1.39499100000000 0.00000000000000 C -1.20809764405066 -0.69749550000000 0.00000000000000 C 1.20809764405066 -0.69749550000000 0.00000000000000 C 1.20809764405066 0.69749550000000 0.00000000000000 H 0.00000000000000 2.49460100000000 0.00000000000000 H -2.16038783830606 1.24730050000000 0.00000000000000 H 0.00000000000000 -2.49460100000000 0.00000000000000 H -2.16038783830607 -1.24730050000000 0.00000000000000 H 2.16038783830607 -1.24730050000000 0.00000000000000 H 2.16038783830606 1.24730050000000 0.00000000000000 End geometry Check $END # Subgroups of D6h include D3h, C6v, D3d, D2h, C2v, C1, etc. This example forces benzene calculation using D2h group. $COMPASS Title C6H6 Molecule test run, cc-pVDZ Basis cc-pVDZ Geometry ... End geometry Check Group D(2h) $END
Nosymm Parameter Type: Boolean
Default: false
Forces BDF to ignore molecular symmetry during the calculation.
Attention
Unlike specifying the C1 group, using this parameter prevents rotation of molecular coordinates. By default, molecular coordinates are rotated to the standard orientation.
Norotate Parameter Type: Boolean
Forces BDF not to rotate molecular coordinates to the standard orientation. Unlike Nosymm, Norotate does not ignore molecular symmetry. However, critical requirement: When symmetry elements like axes or planes are present, their spatial orientation relative to the molecule must exactly match the orientation they would have after rotation to the standard orientation. For example, for a water molecule lying in the yz-plane and symmetric about the xz-plane, BDF would normally rotate it to lie in the xz-plane. Using Norotate forces BDF to calculate with the molecule in the yz-plane while still utilizing its C(2v) symmetry, because the symmetry axis (z-axis) and mirror planes (xz and yz planes) align correctly regardless of the molecular plane (xz or yz). However, if the water molecule lies in the xy-plane, using Norotate will cause an error because its symmetry axis would not be aligned with the z-axis.
Unit Parameter Type: String
Default: Angstrom
Options: Bohr, Angstrom
Specifies the unit of length for input coordinates. Bohr indicates atomic units (Bohr radii), Angstrom indicates Ångstroms.
Skeleton Parameter Type: Boolean
Specifies the symmetry handling method within BDF calculations. BDF offers two approaches to molecular point group symmetry: 1. Traditional: Construct symmetry-adapted orbitals first. Atomic orbital integrals are symmetrized during calculation and stored based on symmetry-adapted orbitals. This method supports non-direct-integral wavefunction theories like SCF, MCSCF, MRCI, CCSD. 2. Skeleton: Only compute and store symmetry-unique atomic orbital integrals (“skeleton integrals”). Symmetry-adapted operators like the J and K matrices are constructed directly during calculations like Hartree-Fock or Kohn-Sham DFT. This “Skeleton” method supports non-Abelian point groups.
Originally, BDF defaulted to the first approach. It now defaults to the second (Skeleton) method. However, Skeleton cannot be used for various post-HF wavefunction theories. Use the Saorb keyword to switch back to the first approach in such cases.
Saorb Parameter Type: Boolean
Specifies the traditional symmetry handling approach (symmetry-adapted orbital construction) within BDF. Required for various post-HF wavefunction theory calculations. See Skeleton keyword.
Extcharge Parameter Type: String
Valid input value: point
Specifies the need for external point charges in the calculation. The external charges are placed in a file named $BDFTASK.extcharge. The file format is:
First line is a title line (can be empty). Second line: An integer N defining the number of additional charges. Third line onwards: N lines defining the charge coordinates and magnitude. Format: Atom Charge x y z
Thresh Parameter Type: String
Default: Medium
Options: Coarse, Medium, Strict
Specifies the precision threshold for determining molecular symmetry. A key feature of BDF is its support for molecular point groups. The compass module automatically identifies the molecular symmetry group and rigorously symmetrizes the molecule accordingly. Due to modeling precision, a molecule might not strictly belong to a particular symmetry point group; this parameter controls the tolerance level for symmetry determination.
$COMPASS Basis cc-pVDZ Geometry C 0.00000000000000 1.39499100000000 0.00000000000000 C -1.20809764405066 0.69749550000000 0.00000000000000 C 0.00000000000000 -1.39499100000000 0.00000000000000 ... End geometry Thresh Medium $END
ExpBas Parameter Type: Integer or String
Options: 0, 1, 2, 3, 4, 5
Prints the basis set and pseudopotentials in the output file using formats compatible with other quantum chemistry programs. Either indices or case-insensitive program names can be specified.
0: Default BDF format
1: Molpro format
2: Molcas format
3: Gaussian format
4: ORCA format
5: CFour format
Uncontract Parameter Type: Boolean
Forces the use of the uncontracted primitive Gaussian basis functions for calculation, regardless of whether the input basis set is contracted. Primarily used for testing.
Primitive Parameter Type: Boolean
Specifies that only primitive Gaussian basis functions in a specific format are input. Primarily used for testing.
Check Parameter Type: Boolean
Prints the most important results in a specific format. Primarily used for testing.
AtomMass Input Block
Specifies isotopic masses for atoms. Input format:
$compass ... Geometry O -1.81084784 -0.11050725 0.00000000 H -2.16957593 0.77995003 0.00000000 K 0.87665046 0.00547937 0.00000000 End Geom AtomMass 2 # Specify masses for 2 atoms. Unspecified atoms use their most abundant isotope mass. 2 2.0 # Specify mass number 2.0 for atom 2 (H) 1 18.0 # Specify mass number 18.0 for atom 1 (O) $end