Gaussian Output

Item	Value
Format ID	g16log
Extensions	.log, .out, .g16, .gal, .irc, .gau
Read	Yes
Write	No
Registry role	Reader
Data level	Coordinates and QM results

Quick read

Python

from molop import AutoParser

frame = AutoParser("calculation.log", parser_detection="g16log")[0][-1]
print(frame.is_normal)
if frame.energies and frame.energies.total_energy is not None:
    print(frame.energies.total_energy.m_as("hartree"))

Output contract

Output is termination status and final total energy, for example True and -317.592366596; the value depends on the file.

See Find fields by scientific property for other results.

MolOP reads Gaussian output files and extracts the data most often needed for computational chemistry post-processing: structures, energies, thermochemistry, vibrations, orbitals, populations, gradients, NMR and response properties, archive records, and termination status. Coverage is described using Gaussian output concepts familiar to computational chemists. “Partial” means common or tested print forms are structured; it is not a claim of complete Gaussian grammar coverage.

Capability	Support	Extracted data	Boundaries
Gaussian job metadata	Example-covered	Software/version metadata, route text, title, charge, multiplicity, and accumulated running time where present.	Fields are normalized; original log line ordering and byte-level layout are not preserved.
Title card	Example-covered	Gaussian title card text as a normalized job title.	Only the title text is advertised; surrounding raw Gaussian formatting is not preserved.
Route keywords and calculation setup	Partial	Raw route text plus recognized model chemistry, job types, dispersion, solvation, population requests, and HF handling.	Method-specific Gaussian keywords outside covered cases may remain raw text.
Input and standard orientations	Example-covered	Atoms and coordinates from input orientation and standard orientation blocks.	Distance-matrix and stoichiometry printouts are not advertised as separate structured fields.
Rotational constants	Example-covered	Rotational constants printed by Gaussian, exposed as frame-level frequency quantities.	Principal-axis diagnostic text is not preserved separately.
SCF and electronic energies	Partial	SCF, Gaussian External, reference/electronic, and method-specific energies; main-log values take precedence over duplicate archive-tail values.	External energies require Gaussian’s External calculation of energy ... / Energy= ... NIter= ... result or an RExternal archive record; not every post-HF or correction energy table is guaranteed structured.
Molecular orbitals and population analysis	Partial	Molecular orbital energies/occupancies; Mulliken charge/spin, APT, Lowdin, Hirshfeld/CM5, NPA, and ESP charge series; electronic spatial extent; multipoles; and early polarizability values where present.	Orbital coefficient matrices, NBO orbital/bond-order details, and schemes without a recognized atomic table are not claimed.
Vibrational frequencies and IR intensities	Partial	Frequencies, reduced masses, force constants, IR intensities, per-mode displacement vectors, and imaginary-mode flags.	Raman, VCD, and other spectrum variants are not advertised unless explicitly covered later.
Thermochemistry	Partial	Temperature, pressure, molecular mass, moments of inertia, rotational symmetry number, rotational/vibrational temperatures, rotational constants, ZPVE, thermal energy, enthalpy, Gibbs free energy, entropy, and heat capacity.	Coverage is mainly tied to frequency-style Gaussian outputs and maintained examples.
Dipole and polarizability	Partial	Dipole and polarizability values from covered Gaussian response-property sections.	Only example-backed response fields are advertised; not every response-property print variant is guaranteed structured.
NMR shielding and spin-spin coupling	Partial	Parses per-atom Gaussian GIAO shielding tensors, observed isotropic/anisotropic and principal values, total K/J coupling matrices, and FC, SD, PSO, and DSO contribution matrices in Hz.	Coverage targets the standard SCF GIAO print family; referenced chemical shifts, EPR, and other gauges are not structured.
Cartesian gradients and forces	Partial	Cartesian force arrays from Gaussian force sections.	Only the normalized force array is advertised; auxiliary force diagnostics are not separately recorded.
Cartesian Hessian	Partial	Cartesian Hessian data from Gaussian second-derivative sections.	The contract is the normalized Hessian field, not every printed second-derivative diagnostic.
Geometry optimization convergence	Partial	Berny optimization summaries, including convergence thresholds, force/displacement values, energy change, and optimized-state flags.	Optimizer diagnostics outside tested examples may remain unstructured.
Gaussian archive section	Partial	Archive-tail metadata, coordinates, energies, thermochemistry, polarizability, and Hessian fallback or augmentation fields.	Main-log fields take precedence where applicable; only explicit RExternal plus archive energy supplies electronic-success evidence, while temperature and pressure are not inferred.
Termination status	Partial	Gaussian termination evidence is segment-scoped and contributes to the file-level aggregate without being copied into frames.	Frame status retains frame-local SCF evidence; detailed failure taxonomy outside structured parse diagnostics is not inferred.
CPU and elapsed time	Example-covered	Job CPU and elapsed-time style records accumulated into the running-time value.	Per-link timing rows are not exposed as separate timing records.
Link1 multi-step jobs	Partial	Link1 section metadata is propagated to later frames so multi-step Gaussian jobs keep the expected per-frame context.	Low-level link boundary rows are not exposed as user-facing records.
Registry conversion	Supported	Parsed Gaussian output can be converted to coordinate and graph formats through the registry.	Conversion quality depends on successful structure and graph recovery.

Gaussian Output Capability Matrix

g16log is a structured reader and does not provide a Gaussian log writer. In the matrix, fakeG indicates whether the field can participate in the Gaussian-like renderer; it does not imply reconstruction of the source log.

Gaussian output content	Parse	Structured target	fakeG	Source fidelity	Current boundary
Gaussian software and version	Fixture-covered	qm_software, qm_software_version	Supported	Unsupported	Maintained Gaussian version banners are covered; an exact version cannot be inferred from a truncated file without a header.
Link0/options	Partial	File/frame options text	Supported	Unsupported	Printed Link0 options are stored; fakeG can derive a CPU line from %nprocshared, but complete structured resource projection is not guaranteed.
Route and title	Fixture-covered	keywords, title_card, semantic_route	Supported	Unsupported	Route semantics are shared with GJF; title and route are normalized without decorative lines.
Method, functional, basis, and tasks	Partial	model_chemistry, task_requests, and compatibility fields	Partial	Not applicable	Only shared-route keywords are structured; requested properties are never fabricated solely from the route.
Charge and multiplicity	Supported	Frame/file top-level fields	Supported	Unsupported	Extracted from Gaussian charge/multiplicity lines or archive metadata; main-log values take priority.
Link1 / multi-segment context	Partial	Segment/frame indices and propagated task metadata	Partial	Unsupported	Applicable section metadata propagates to later frames; low-level Link enter/leave rows are not public business records.
Input orientation	Fixture-covered	atoms, coords	Supported	Unsupported	Coordinates are normalized without preserving table whitespace or center numbers.
Standard orientation	Fixture-covered	standard_coords, transformation matrix	Supported	Unsupported	The input/standard rigid transform can be computed; standard orientation may backfill coordinates when input orientation is absent.
Structure-only fast parsing	Supported	Atoms, coordinates, and basic frame data	Not applicable	Not applicable	only_extract_structure stops after orientation and skips energies, frequencies, thermochemistry, and other expensive fields.
Rotational constants	Fixture-covered	rotation_constants	Raw/limited	Unsupported	Exposed as a GHz array; fakeG has no complete canonical rotational-constant renderer.
SCF/reference energy	Supported	energies.reference_energy, energy observations	Supported	Unsupported	Extracted from SCF Done, a successful Gaussian External energy result, or its RExternal archive record; fakeG emits E(SCF) without the original method label or cycle history.
MP2, MP3, MP4, MP5	Partial	energies.mp*_energy	Unsupported	Unsupported	Covered EUMP*/MP5 lines parse; all MP corrections and spin-component tables are not guaranteed.
CCSD and CCSD(T)	Partial	energies.ccsd_energy, ccsd_t_energy	Unsupported	Unsupported	Covered total-energy lines parse; other coupled-cluster variants and correction tables are not guaranteed.
Archive energy fallback	Partial	Merged energies	Indirect	Unsupported	Main-log observations take priority; archive values augment missing or duplicate fields without overriding stronger live evidence.
Total spin	Partial	total_spin.spin_square, spin_quantum_number	Supported	Unsupported	Only standard S**2 / S print forms are covered.
MO energies, occupations, and symmetry	Partial	molecular_orbitals	Raw/unsupported	Unsupported	Alpha/beta, open-shell, and concatenated-number regressions are covered; complete MO coefficient matrices are not parsed.
Mulliken charge / spin populations	Partial	charge_spin_populations	Raw/unsupported	Unsupported	Separate and combined open-shell charge/spin tables are structured; headings, sums, and source precision are not retained.
APT / Lowdin populations	Partial	charge_spin_populations	Raw/unsupported	Unsupported	Coverage is limited to standard tables in maintained examples.
Hirshfeld / CM5	Partial	populations["hirshfeld_charges"], populations["hirshfeld_spins"], populations["cm5_charges"]	Raw/unsupported	Unsupported	Hirshfeld charge/spin and CM5 charge series parse.
NPA / ESP atomic charges	Partial	populations["npa_charges"], populations["esp_charges"]	Raw/unsupported	Unsupported	The last complete NPA summary and ESP atomic charge table in a frame are retained; detailed NBO orbitals and bond orders are not parsed.
Electronic spatial extent	Partial	polarizability.electronic_spatial_extent	Raw/unsupported	Unsupported	Only the standard scalar line in population output is covered.
Dipole and higher multipoles	Partial	Dipole, quadrupole, traceless quadrupole, octapole, and hexadecapole fields	Raw/unsupported	Unsupported	Covered field-independent/response forms parse; all units and frequency-dependent variants are not guaranteed.
Polarizability	Partial	Isotropic, anisotropic, and tensor fields	Raw/unsupported	Unsupported	Population, response, and archive sources merge; later explicit response data may replace an earlier approximation.
Harmonic frequencies	Partial	vibrations.frequencies, imaginary-mode flags	Supported	Unsupported	Concatenated numeric output is handled; anharmonic/VPT2 result tables are not parsed.
Reduced mass, force constant, and IR	Partial	Corresponding vibrations arrays	Supported	Unsupported	Values align by mode; Raman activity and VCD/ROA are not in the structured contract.
Normal-mode displacement	Partial	vibrations.vibration_modes and axis metadata	Supported	Unsupported	Normalized to mode/atom/Cartesian; normalization and mass weighting remain unknown.
Temperature and pressure	Partial	Frame temperature, pressure	Supported	Unsupported	Read from standard frequency/thermochemistry lines; archive data does not invent absent temperature or pressure.
Molecular mass, inertia, and rotational data	Partial	thermal_informations	Supported	Unsupported	Covers mass, moments, symmetry number, rotational temperatures, and rotational constants.
Vibrational temperatures	Partial	vibrational_temperatures and mode indices	Supported	Unsupported	Positive-frequency modes are mapped first; only demonstrable array relations are retained when counts disagree.
ZPVE and thermal corrections	Partial	ZPVE/TCE/TCH/TCG in thermal_informations	Supported	Unsupported	Values use normalized Hartree/particle units; all partition-function diagnostics are not included.
U0, UT, H, G, entropy, and Cv	Partial	thermal_informations	Supported	Unsupported	Standard Gaussian thermochemistry summaries parse; source pretty-print layout is not modeled.
Cartesian forces	Partial	forces plus axis/order/orientation metadata	Raw/unsupported	Unsupported	Shape is (N, 3) in source atom order; orientation is normally unknown.
Cartesian Hessian	Partial	hessian plus axis/order/orientation metadata	Raw/unsupported	Unsupported	Main second-derivative data take priority and archive can backfill; shape must be (3N, 3N).
Berny convergence	Partial	geometry_optimization_status	Supported	Unsupported	Force/displacement values, thresholds, energy change, and optimized state are covered; other optimizers may remain unstructured.
SCF and termination status	Partial	Frame-local status, segment/file aggregate status	Synthetic	Unsupported	SCF evidence is frame-local; normal/error termination is segment/file scoped. fakeG termination is not source-status reproduction.
CPU / elapsed time	Fixture-covered	Accumulated running_time	Partial	Unsupported	File totals aggregate segments; per-Link timing records are not public, and multiframe fakeG removes frame runtime lines.
Archive-tail metadata/coordinates	Partial	Missing-field fallback	Indirect	Unsupported	Archive can augment metadata, coordinates, energies, thermochemistry, polarizability, and Hessian; live data take priority.
TD excited-state results	Unsupported	No stable public result contract	Unsupported	Unsupported	The route may identify a TD request, but excitation energies and oscillator strengths are not structured.
NMR magnetic shielding	Partial	nmr.gauge, per-atom shielding_tensors, isotropic, anisotropy, and principal values	Unsupported	Unsupported	Covers standard SCF GIAO (ppm) output; tensors align by source atom index and Cartesian orientation is currently unknown. Per-atom shielding values can be projected into RDKit atom properties with qm_embedded_rdmol(embed_nmr=True).
NMR spin-spin coupling	Partial	spin_spin_coupling_k, spin_spin_coupling_j, spin_spin_coupling_k_components, spin_spin_coupling_j_components, and coupling_atom_indices	Unsupported	Unsupported	Expands blockwise lower-triangle total and FC/SD/PSO/DSO K/J tables into symmetric Hz matrices; coupling matrices remain frame-level atom-pair data.
EPR, referenced chemical shifts, NBO bond orders, and other specialized results	Unsupported	No stable public result contract	Unsupported	Unsupported	A route request does not imply result coverage; each property requires fixtures and a public semantic contract.
Coordinate/graph conversion	Supported	Frame structure / recovered graph	Not applicable	Not applicable	Coordinate conversion requires extracted structure; graph conversion also depends on bond-order and charge-state recovery.
Lossless source-log rewriting	Unsupported	Component raw snippets are inspection/fallback only	Unsupported	Unsupported	The parser is a field extractor, not a complete Gaussian-output CST, and has no byte-for-byte writer.

capture_source_evidence=True retains source evidence for energies, SCF status, and optimization convergence for audit-oriented workflows. Default parsing focuses on result extraction. Neither mode preserves the complete original output structure.