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W1 Methods

These method keywords request the W1 methods of Martin [Martin99, Parthiban01]:

  • The W1U keyword specifies the W1 method modified to use UCCSD instead of ROCCSD for open shell systems [Barnes09] (the ROCCSD method is that of Handy, Pople and coworkers [Knowles91]).
  • W1BD requests a related method which replaces coupled cluster with BD [Barnes09]. 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] with a slightly improved scalar relativistic correction as described in [Barnes09].

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 W1BD.

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).

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 W1BD calculation:

 Results before spin correction.
 Temperature=         298.150000 Pressure=                 1.000000
 E(ZPE)=                0.016919 E(Thermal)=               0.019783
 W1BD (0 K)=          -39.139927 W1BD  Energy=           -39.137063
 W1BD  Enthalpy=      -39.136119 W1BD  Free Energy=      -39.158277

 W1U 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).

 DE(Spin)=                         -0.000051

 W1Bsc Electronic Energy           -39.156897 	Predicted energy.

 Spin-corrected results.
 Temperature=         298.150000 Pressure=                 1.000000
 E(ZPE)=                0.016919 E(Thermal)=               0.019783
 W1Bsc(0 K)=          -39.139978 W1Bsc Energy=           -39.137114
 W1Bsc Enthalpy=      -39.136170 W1Bsc Free Energy=      -39.158328

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):

W1Bsc (0 K)    Zero-point-corrected electronic energy: E0 = Eelec + ZPE
W1Bsc Energy    Thermal-corrected energy: E = E0 + Etrans + Erot + Evib
W1Bsc Enthalpy    Enthalpy computed using the spin-corrected W1BD predicted energy: H = E + RT
W1Bsc Free Energy    Gibbs Free Energy computed using the spin-corrected W1BD predicted energy: G = H – TS

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