Gaussian has been designed with the needs of the user in mind. All of the standard input is free-format and mnemonic. Reasonable defaults for input data have been provided, and the output is intended to be self-explanatory. Mechanisms are available for the sophisticated user to override defaults or interface their own code to the Gaussian system. The authors hope that their efforts will allow users to concentrate their energies on the application of the methods to chemical problems and to the development of new methods, rather than on the mechanics of performing the calculations.
The technical capabilities of the Gaussian 03 system are listed in the subsections below.
Calculation of one- and two-electron integrals over any general contracted gaussian functions. The basis functions can either be cartesian gaussians or pure angular momentum functions, and a variety of basis sets are stored in the program and can be requested by name. Integrals may be stored in memory, stored externally, or be recomputed as needed [20,21,22,23,24,25,26,27,28]. The cost of computations can be linearized using fast multipole method (FMM) and sparse matrix techniques for certain kinds of calculations [29,30,31,32,33,34].
Transformation of the atomic orbital (AO) integrals to the molecular orbital basis by "in-core" means (storing the AO integrals in memory), "direct" means (no integral storage required), "semi-direct" means (using some disk storage of integrals), or "conventional" means (with all AO integrals on disk).
Use of density fitting to speed up the Coulomb part of pure DFT calculations [35,36].
Numerical quadrature to compute DFT XC energies and their derivatives.
Molecular mechanics calculations using the AMBER [37], DREIDING [38] and UFF [39,40] force fields.
Semi-empirical calculations using the CNDO [41], INDO [42], MINDO/3 [43,44], MNDO [43,45,46,47,48,49,50,51,52], AM1 [43,48,49,53,54], and PM3 [55,56] model Hamiltonians.
Self-consistent field calculations using closed-shell (RHF) [57], unrestricted open-shell (UHF) [58], and restricted open-shell (ROHF) [59] Hartree-Fock wavefunctions.
Correlation energy calculations using Møller-Plesset perturbation theory [60] carried to second, third [61], fourth [62,63], or fifth[64] order. MP2 calculations use direct [21,65] and semi-direct methods [23] to use efficiently however much (or little) memory and disk are available.
Correlation energy calculations using configuration interaction (CI), using either all double excitations (CID) or all single and double excitations (CISD) [66].
Coupled cluster theory with double substitutions (CCD)[67], coupled cluster theory with both single and double substitutions (CCSD) [68,69,70,71], Quadratic Configuration Interaction using single and double substitutions (QCISD) [72], and Brueckner Doubles Theory (BD) [73,74]. A non-iterative triples contribution may also be computed (as well as quadruples for QCISD and BD).
Density functional theory [75,76,77,78,79], including general, user-configurable hybrid methods of Hartree-Fock and DFT. See this page for a complete list of available functionals.
Automated, high accuracy energy methods: G1 theory [80,81], G2 theory [82], G2(MP2) [83] theory, G3 theory [84], G3(MP2) [85], and other variants [86]; Complete Basis Set (CBS) [87,88,89,90,91] methods: CBS-4 [91,92], CBS-q [91], CBS-Q [91], CBS-Q//B3 [92,93], and CBS-QCI/APNO [90], as well as general CBS extrapolation; the W1 method of Martin (with slight modifications) [94,95,96].
General MCSCF, including complete active space SCF (CASSCF) [97,98,99,100], and allowing for the optional inclusion of MP2 correlation [101]. Algorithmic improvements [102] allow up to 14 active orbitals in Gaussian 03. The RASSCF variation is also supported [103,104].
The Generalized Valence Bond-Perfect Pairing (GVB-PP) SCF method [105].
Testing the SCF wavefunctions for stability under release of constraints, for both Hartree-Fock and DFT methods [106,107].
Excited state energies using the single-excitation Configuration Interaction (CI-Singles) method [108], the time-dependent method for HF and DFT [109,110,111], the ZINDO semi-empirical method [112,113,114,115,116,117,118,119,120], and the Symmetry Adapted Cluster/Configuration Interaction (SAC-CI) method of Nakatsuji and coworkers [121,122,123,124,125,126,127,128,129,130,131,132,133,134,135].
Analytic computation of the nuclear coordinate gradient of the RHF [136], UHF, ROHF, GVB-PP, CASSCF [137,138], MP2 [22,23,139,140], MP3, MP4(SDQ) [141,142], CID [143], CISD, CCD, CCSD, QCISD, Density Functional, and excited state CIS energies [108]. All of the post-SCF methods can take advantage of the frozen-core approximation.
Automated geometry optimization to either minima or saddle points [136,144,145,146,147,148], using internal or cartesian coordinates or a mixture of coordinates. Optimizations are performed by default using redundant internal coordinates [149], regardless of the input coordinate system used.
Automated transition state searching using synchronous transit-guided quasi-Newton methods [150].
Reaction path following using the intrinsic reaction coordinate (IRC) [151,152].
Two- or three-layer ONIOM [153,154,155,156,157,158,159,160,161,162,163] calculations for energies and geometry optimizations.
Simultaneous optimization of a transition state and a reaction path [164].
Conical intersection optimization using state-averaged CASSCF [165,166,167].
IRCMax calculation which locates the point of maximum energy for a transition structure along a specified reaction path [168,169,170,171,172,173,174,175,176].
Classical trajectory calculation in which the classical equations of motion are integrated using analytical second derivatives [177,178,179,180] using either:
Born Oppenheimer molecular dynamics (BOMD) [177,178,179,180,181,182] (see [183] for a review) [184,185,186,187,188]. This can be done using any method for which analytic gradients are available, and can optionally make use of Hessian information.
Propagation of the electronic degrees of freedom via the Atom Centered Density Matrix Propagation molecular dynamics model [188,189,190]. This method has similarity and differences to the related Car-Parrinello approach [191]. See the discussion of the ADMP keyword for details. This can be done using the AM1, HF, and DFT methods.
Analytic computation of force constants (nuclear coordinate second derivatives), polarizabilities, hyperpolarizabilities, and dipole derivatives analytically for the RHF, UHF, DFT, RMP2, UMP2, and CASSCF methods [25,139,192,193,194,195,196,197,198,199], and for excited states using CIS.
Numerical differentiation of energies or gradients to produce force constants, polarizabilities, and dipole derivatives for the MP3, MP4(SDQ), CID, CISD, CCD, and QCISD methods [143,200,201,202].
Harmonic vibrational analysis and thermochemistry analysis using arbitrary isotopes, temperature, and pressure.
Analysis of normal modes in internal coordinates.
Determination of IR and Raman intensities for vibrational transitions [193,194,196,200,203]. Pre-resonance Raman intensities are also available.
Anharmonic vibration and vibration-rotation coupling [204,206,207,208,209,210,211,212,213,214]. Anharmonic vibrations are available for the methods for which analytic second derivatives are available.
Evaluation of various one-electron properties using the SCF, DFT, MP2, CI, CCD and QCISD methods, including Mulliken population analysis [215], multipole moments, natural population analysis, electrostatic potentials, and electrostatic potential-derived charges using the Merz-Kollman-Singh [216,217], CHelp [218], or CHelpG [219] schemes.
Static and frequency-dependent polarizabilities and hyperpolarizabilities for Hartree-Fock and DFT methods [220,221,222,223,224,225].
NMR shielding tensors and molecular susceptibilities using the SCF, DFT and MP2 methods [226,227,228,229,230,231,232,233,234,235]. Susceptibilities can now be computed using GIAOs [236,237]. Spin-spin coupling constants can also be computed [238,239,240,241] at the Hartree-Fock and DFT levels.
Vibrational circular dichroism (VCD) intensities [242].
Propagator methods for electron affinities and ionization potentials [243,244,245,246,247,248,249].
Approximate spin orbit coupling between two spin states can be computed during CASSCF calculations [250,251,252,253,254].
Electronic circular dichroism [255,256,257,258,259] (see [260] for a review).
Optical rotations and optical rotary dispersion via GIAOs [261,262,263,264,265,266,267,268,269,270,271].
Hyperfine spectra: g tensors, nuclear electric quadrupole constants, rotational constants, quartic centrifugal distortion terms, electronic spin rotation terms, nuclear spin rotation terms, dipolar hyperfine terms, and Fermi contact terms [272,273,274,275,276,277,278,279]. Input can be prepared for the widely used program of H. M. Pickett [280].
All of these models employ a self-consistent reaction field (SCRF) methodology for modeling systems in solution.
Onsager model (dipole and sphere) [281,282,283,284], including analytic first and second derivatives at the HF and DFT levels, and single-point energies at the MP2, MP3, MP4(SDQ), CI, CCD, and QCISD levels.
Polarized Continuum (overlapping spheres) model (PCM) of Tomasi and coworkers [285,286,287,288,289,290,291,292,293,294,295,296,297,298,299,300,301,302,303] for analytic HF, DFT, MP2, MP3, MP4(SDQ), QCISD, CCD, CCSD, CID, and CISD energies and HF and DFT gradients and frequencies.