Description
These method keywords request the W1 methods of Martin [ Martin99 J. M. L. Martin and G. de Oliveira, “Towards standard methods for benchmark quality ab initio thermochemistry - W1 and W2 theory,” J. Chem. Phys., 111 (1999) 1843-56. DOI: , Parthiban01 S. Parthiban and J. M. L. Martin, “Assessment of W1 and W2 theories for the computation of electron affinities, ionization potentials, heats of formation, and proton affinities,” J. Chem. Phys., 114 (2001) 6014-29. DOI: ]:
- The W1U keyword specifies the W1 method modified to use UCCSD instead of ROCCSD for open shell systems [ Barnes09 E. C. Barnes, G. A. Petersson, J. A. Montgomery Jr., M. J. Frisch, and J. M. L. Martin, "Unrestricted Coupled Cluster and Brueckner Doubles Variations of W1 Theory," J. Chem. Theor. Comput., 5 (2009) 2687. DOI: ] (the ROCCSD method is that of Handy, Pople and coworkers [ Knowles91 P. J. Knowles, J. S. Andrews, R. D. Amos, N. C. Handy, and J. A. Pople, “Restricted Møller-Plesset theory for open shell molecules,” Chem. Phys. Lett., 186 (1991) 130-36. DOI: ]).
- W1BD requests a related method which replaces coupled cluster with BD [ Barnes09 E. C. Barnes, G. A. Petersson, J. A. Montgomery Jr., M. J. Frisch, and J. M. L. Martin, "Unrestricted Coupled Cluster and Brueckner Doubles Variations of W1 Theory," J. Chem. Theor. Comput., 5 (2009) 2687. DOI: ]. This method is both more expensive and more accurate than CBS-QB3 and G3 (true for all W1 methods); we recommend using W1BD when you require very accurate energies.
- W1RO is the W1 method described in [ Martin99 J. M. L. Martin and G. de Oliveira, “Towards standard methods for benchmark quality ab initio thermochemistry - W1 and W2 theory,” J. Chem. Phys., 111 (1999) 1843-56. DOI: ] with a slightly improved scalar relativistic correction as described in [ Barnes09 E. C. Barnes, G. A. Petersson, J. A. Montgomery Jr., M. J. Frisch, and J. M. L. Martin, "Unrestricted Coupled Cluster and Brueckner Doubles Variations of W1 Theory," J. Chem. Theor. Comput., 5 (2009) 2687. DOI: ].
オプション
Options
SP
Perform only a single-point energy evaluation using the specified compound model chemistry. No zero-point or thermal energies are included.
NoOpt
Perform the frequencies and single-point energy calculation for the specified model chemistry at the input geometry. Freq=TProjected is implied. This option is not meaningful or accepted for methods such as G1, which use different geometries for the frequencies and the single-point steps. StartFreq is a synonym for NoOpt.
ReadAmplitudes
Reads the converged amplitudes from the checkpoint file (if present). Note that the new calculation can use a different basis set, method (if applicable), etc. than the original one.
SaveAmplitudes
Saves the converged amplitudes in the checkpoint file for use in a subsequent calculation (e.g., using a larger basis set). Using this option results in a very large checkpoint file, but also may significantly speed up later calculations.
The ReadAmplitudes option is the default for all W1 methods. SaveAmplitudes is also the default for W1U.
Restart
Restart an incomplete W1 calculation.
ReadIsotopes
This option allows you to specify alternatives to the default temperature, pressure, frequency scale factor and/or isotopes—298.15 K, 1 atmosphere, no scaling, and the most abundant isotopes (respectively). It is useful when you want to rerun an analysis using different parameters from the data in a checkpoint file.
Be aware, however, that all of these can be specified in the route section (Temperature, Pressure and Scale keywords) and molecule specification (the Iso parameter), as in this example:
#T Method/6-31G(d) JobType Temperature=300.0 … … 0 1 C(Iso=13) …
ReadIsotopes input has the following format:
| temp pressure [scale] | Values must be real numbers. |
| isotope mass for atom 1 | |
| isotope mass for atom 2 | |
| … | |
| isotope mass for atom n |
Where temp, pressure, and scale are the desired temperature, pressure, and an optional scale factor for frequency data when used for thermochemical analysis (the default is unscaled). The remaining lines hold the isotope masses for the various atoms in the molecule, arranged in the same order as they appeared in the molecule specification section. If integers are used to specify the atomic masses, the program will automatically use the corresponding actual exact isotopic mass (e.g., 18 specifies 18O, and Gaussian uses the value 17.99916).
実例
Examples
Calculation Summary Output. After all of the output for the component job steps, Gaussian prints a table of results for these methods. Here is the key part of the output from a W1U calculation on an open shell system:
Results before spin correction. W1U Electronic Energy -39.843586 Temperature= 298.150000 Pressure= 1.000000 E(ZPE)= 0.029216 E(Thermal)= 0.032275 W1U (0 K)= -39.814370 W1U Energy= -39.811312 W1U Enthalpy= -39.810367 W1U Free Energy= -39.833116 W1U spin correction: Reference for spin correction: G.P.F. Wood, L. Radom, G.A. Petersson, E.C. Barnes, M.J. Frisch and J.A. Montgomery, Jr., JCP 125, 94106 (2006). Spin-corrected results. DE(Spin)= -0.000074 W1Usc Electronic Energy -39.843660 Temperature= 298.150000 Pressure= 1.000000 E(ZPE)= 0.029216 E(Thermal)= 0.032275 W1Usc(0 K)= -39.814444 W1Usc Energy= -39.811386 W1Usc Enthalpy= -39.810441 W1Usc Free Energy= -39.833190
The predicted energy is given between the ordinary and spin-corrected thermochemistry analysis tables.
The energy labels thus have the following meanings (spin-corrected W1BD is used as an example):
| W1Usc (0 K) | Zero-point-corrected electronic energy: E0 = Eelec + ZPE | |
| W1Usc Energy | Thermal-corrected energy: E = E0 + Etrans + Erot + Evib | |
| W1Usc Enthalpy | Enthalpy computed using the spin-corrected W1U predicted energy: H = E + RT | |
| W1Usc Free Energy | Gibbs Free Energy computed using the spin-corrected W1U predicted energy: G = H – TS |