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Terms Of Reference

The computational basis or computational order is the order of centers and basis functions used by the integral package, and thus the rest of the calculation.

The ZMAT basis or ZMAT order refers to centers arranged in the order of the user's ZMAT file. Basis functions are rearranged to correspond to the ZMAT center ordering and may be further rearranged within a center to facilitate symmetry checking operations.

For transformation matrices, we try to indicate which bases label the rows and columns of the matrix in order to avoid confusion in their application. For non-unitary transformations, we also specify which side the transformation acts on.

SOs are symmetry-adapted orbitals, the basis in which the bulk of CFOUR operates. AOs are atomic orbitals which are used mainly for symmetry analysis within the codes.

The sizes of records are described symbolically using the following definitions:

NAO Number of atomic orbitals
NMO Number of molecular orbitals
NAtoms Number of centers specified in the ZMAT
NRX Number of degree of freedoms of the molecule
NIrreps Number of irreps in computational point group
NOrbits Number of orbits'' (symmetry-unique centers)
NSO Number of symmetry-adapted orbitals

The actual variables employed in the code may be different.

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CFOUR is partially supported by the U.S. National Science Foundation.