Topologies and residues¶

This page contains the full reference for topologies and residues. The input format page provides a high-level summary with minimal examples.

topologies¶

topologies is an array of topology objects. Each topology contains the molecular data, fragmentation, and connectivity for a single system. Batched mode is achieved by listing multiple topologies with a shared driver/model/keywords configuration.

topology fields¶

Field	Type	Required	Notes
`schema_version`	string	No	Defaults to `0.2.0`.
`symbols`	array of string	Yes*	Atomic symbols (“H”, “C”, etc). Required if `xyz` is not provided.
`geometry`	array of float	Yes*	Flat XYZ array (length = 3 * atoms). Required if `xyz` is not provided.
`xyz`	string	Yes*	Path to XYZ file; EXESS will read it instead of `symbols` + `geometry`.
`velocities`	array of float	No	Flat XYZ velocity array (Angstrom/ps).
`labels`	array of string	No	Atom labels.
`partial_charges`	array of float	No	Per-atom partial charges.
`formal_charges`	array of int	No	Per-atom formal charges. Defaults to 0 for all atoms.
`connectivity`	array of bonds	No	Bond list for covalent fragmentation.
`stereochemistry`	array of int	No	One entry per bond.
`fragments`	array of arrays	No	Zero-indexed atom indices per fragment. If omitted, EXESS assumes a single fragment containing all atoms.
`fragment_formal_charges`	array of int	No	Per-fragment formal charges. Defaults to 0 per fragment if omitted.
`fragment_partial_charges`	array of float	No	Per-fragment partial charges.
`fragment_multiplicities`	array of int	No	Per-fragment multiplicities (open-shell systems). Defaults to 1 per fragment if omitted.
`waters`	array of two ints	No	First/last water molecule treated classically.

Inputs require either symbols + geometry or xyz, but not both.

Notes:

labels can be used to annotate specific atoms (e.g., alpha carbons in residues).
partial_charges, formal_charges, and labels must match the length of symbols if provided.
connectivity is a perceived bond list and should not be treated as a definitive source of bond information.
stereochemistry is only valid if connectivity is present and must match its length.
velocities are used for dynamics; they are present only in v1 inputs but are supported.
fragments must include each atom exactly once when provided.
rush-py expects topology JSON inputs (symbols + geometry). It does not accept xyz paths.

geometry¶

Example layout:

"geometry": [
  -4.3997, 1.0764, 7.7009,
  -3.9597, 0.2664, 7.3109,
  -4.4297, 0.9964, 8.7009
]

symbols¶

"symbols": ["O", "H", "H"]

xyz¶

xyz can be used instead of geometry and symbols, including for fragmented systems (it is compatible with fragmentation keywords). Standard XYZ files begin with the atom count, followed by a comment line and then element + XYZ positions:

3

O -1.1570 0.0630 -0.4817
H -1.1570 0.8180 -1.0766
H -1.1570 -0.6920 -1.0766

Example usage in EXESS:

{
  "topologies": [
    { "xyz": "/path/to/water.xyz" }
  ]
}

connectivity¶

Connectivity is required when a covalent bond is broken across fragments. EXESS will add hydrogen caps to satisfy valences and remove them after the calculation.

A bond entry is [atom_index_1, atom_index_2, bond_order].

EXESS defines the following bond order values (single/double/triple bonds are the most common values):

0: Unspecified
1: Single
2: Double
3: Triple
4: Quadruple
5: Quintuple
6: Sextuple
250: FiveAndAHalf
251: FourAndAHalf
252: ThreeAndAHalf
253: TwoAndAHalf
254: OneAndAHalf
255: Ring

Example:

"connectivity": [
  [1, 4, 1],
  [9, 12, 1]
]

A covalent fragmentation example with two ethane fragments connected across a C-C bond uses connectivity: [[1, 4, 1]] to signal a single bond between atom indices 1 and 4. EXESS uses this information to apply hydrogen caps on broken valences during fragmentation and removes them after the calculation.

stereochemistry¶

EXESS accepts a list of integers aligned with the connectivity list:

0: None
1: Up
-1: Down
2: Either
3: CisOrTrans

fragments¶

Fragment indices are zero-indexed. Example for five water fragments:

"fragments": [
  [0, 1, 2],
  [3, 4, 5],
  [6, 7, 8],
  [9, 10, 11],
  [12, 13, 14]
]

fragment_formal_charges / fragment_multiplicities¶

If fragment_formal_charges is omitted, EXESS sets fragment charges to the sum of per-atom formal_charges when provided, otherwise 0.
If fragment_multiplicities is omitted, EXESS sets multiplicity to 1 for every fragment.
If fragments is omitted, EXESS assumes a single fragment containing all atoms and derives defaults accordingly.

Example for a single, unfragmented system:

{
  "topologies": [
    {
      "geometry": [
        -4.3997, 1.0764, 7.7009,
        -3.9597, 0.2664, 7.3109,
        -4.4297, 0.9964, 8.7009
      ],
      "symbols": ["O", "H", "H"],
      "fragment_formal_charges": [0],
      "fragment_multiplicities": [1]
    }
  ]
}

topology validation checks¶

Validation checks when constructing inputs:

geometry must be length 3 * len(symbols).
labels, partial_charges, and formal_charges must match symbols length if present.
connectivity atom indices must be valid and may not reference the same atom twice.
stereochemistry is only valid when connectivity is present and must be the same length.
velocities must be length 3 * len(symbols) if present.
fragments must not duplicate atoms; each atom should appear in exactly one fragment.
fragment_formal_charges, fragment_partial_charges, and fragment_multiplicities must match fragments length when provided.

waters¶

waters is a two-element array identifying the first and last water molecule to be treated classically (used by some QMMM/Q4ML workflows).

residues¶

residues is an optional array of residue definitions used for TRC-based workflows and QMMM. Each element is a Residues object:

Field	Type	Notes
`labeled`	array[int]	Optional list of residue indices with labels.
`labels`	array of array[string]	Optional labels per residue.
`residues`	array of array[int]	Atom indices per residue.
`seqs`	array[string]	Residue names.
`seq_ns`	array[int]	Residue numbers.
`insertion_codes`	array[string]	Required PDB-style insertion codes (use empty strings when not applicable).

residues is typically aligned one-to-one with topologies (same index). It is required for QMMM and other workflows that rely on residues, and it is often generated by converting PDB/TRC inputs. insertion_codes is required; use empty strings when there are no insertion codes.