G2(MP2) Theory
G2(MP2) theory is a substantially cheaper variation of G2 with only slightly
reduced predictive power. The G2(MP2) energy at 0 degrees Kelvin E0(G2MP2)
is defined as:
The definition of the components being:
The necessary energies can be calculated most efficiently in the following sequence:
- Optimization and frequency calculation at the HF/6-31G(d) level of theory
- Optimization at the MP2(FULL)/6-31G(d) level of theory
- QCISD(T,FC)/6-311G(d,p)//MP2(FULL)/6-31G(d) single point
- MP2(FC)/6-311+G(3df,2p)//MP2(FULL)/6-31G(d) single point
The G2MP2 keyword can be used in Gaussian in order to
compute all required energy components
in an orderly manner.
Comments:
- Open shell systems are treated using unrestricted wavefunctions (UHF, UMP2 . . )
- The higher level correction (HLC) is supposed to compensate remaining deficiencies
of the method. The A value has been chosen such that the energy of the hydrogen atom
is exact. The B value has been chosen such as to minimize the error for the predicted
heat of formation of 55 known molecules.
- The mean absolute deviation for the original G2 neutral set (125 reaction energies)
is 1.58 kcal/mol. The mean absolute deviation for the extended G2 neutral set (148 reaction
energies) is 2.04 kcal/mol.
Literature:
- L. A. Curtiss, K. Raghavachari, G. W. Trucks, J. A. Pople,
"Gaussian-2 theory for molecular energies of first- and second-row compounds"
J. Chem. Phys. 1991, 94, 7221 - 7230.
- L. A. Curtiss, J. E. Carpenter, K. Raghavachari, J. A. Pople
"Validity of additivity approximations used in Gaussian-2 theory"
J. Chem. Phys. 1992, 96, 9030 - 9034.
- L. A. Curtiss, K. Raghavachari, J. A. Pople,
"Gaussian-2 theory using reduced Møller-Plesset orders"
J. Chem. Phys. 1993, 98, 1293 - 1298.
- M. Glukhovtsev, A. Pross, M. McGrath, L. Radom,
"Extension of Gaussian-2 (G2) theory to bromine- and iodine-containing molecules:
Use of effective core potentials"
J. Chem. Phys. 1995, 103, 1878.
- L. A. Curtiss, P. C. Redfern, B. J. Smith, L. Radom,
"Gaussian-2 (G2) theory: Reduced basis set requirements"
J. Chem. Phys. 1996, 104, 5148.
last changes: 01.04.2008, AS
questions & comments to: axel.schulz@uni-rostock.de