 


Example 1: P3+ / 6311G(2df,2pd) calculations of vertical
ionization potentials (VIPs) of water molecule
Input to G16 program:
#p ept(p3,ReadOrbitals) 6311G(2df,2pd)
Title: P3+ calculations for VIPs of water.
0 1
H
O 1 0.957
H 2 0.957 1 104.2
2 4
The option ept(p3,ReadOrbitals) invokes the EPT calculations in the
renormalized partial thirdorder (P3+) approximation and requests the program
to read an additional line (the last line of the input) containing orbitals for
which electron binding energies will be calculated. In this case, these are
orbitals 2 through 4, where numbering starts with the first correlated
orbital. As the standard frozencore approximation is a default in Gaussian
calculations (in this case one lowestenergy occupied orbital is frozen),
the line 2 4 requests a calculation of vertical electron detachment
energies (VEDEs)
for HOMO2, HOMO1, and HOMO orbitals. The resulting output gives these
VEDEs as:
Summary of results for alpha spinorbital 2 P3:
Koopmans theorem: 0.70477D+00 au 19.178 eV
Converged second order pole: 0.66713D+00 au 18.153 eV 0.921 (PS)
Converged 3rd order P3 pole: 0.68842D+00 au 18.733 eV 0.939 (PS)
Renormalized (P3+) P3 pole: 0.68535D+00 au 18.649 eV 0.936 (PS)
Summary of results for alpha spinorbital 3 P3:
Koopmans theorem: 0.57443D+00 au 15.631 eV
Converged second order pole: 0.50721D+00 au 13.802 eV 0.905 (PS)
Converged 3rd order P3 pole: 0.53772D+00 au 14.632 eV 0.930 (PS)
Renormalized (P3+) P3 pole: 0.53273D+00 au 14.496 eV 0.926 (PS)
Summary of results for alpha spinorbital 4 P3:
Koopmans theorem: 0.50156D+00 au 13.648 eV
Converged second order pole: 0.42117D+00 au 11.460 eV 0.899 (PS)
Converged 3rd order P3 pole: 0.45510D+00 au 12.384 eV 0.926 (PS)
Renormalized (P3+) P3 pole: 0.44939D+00 au 12.228 eV 0.921 (PS)
Note that besides the P3+ number, results are also reported for lowerorder
approximations, namely Koopmans's theorem (which is simply equal to the orbital
energy), diagonal secondorder method (D2) and partial thirdorder (P3) method.
The last column contains the pole strength
(PS) values. PS is equal to the norm of a Dyson orbital corresponding to a
given VEDE and is calculated from a residue at this VEDE.
PS values below 0.85 indicate that the diagonal selfenergy
approximations (i.e., D2, D3, OVGF, P3, P3+)
are unreliable!!!
Sign convention:
Numbers reported above are VEDEs
defined as the total energy of the Nelectron system minus the
total energy of the (N1)electron system. A negative value of VEDE
therefore means that the Nelectron system is bound. VIP is a negative of
VEDE and hence all above examples correspond to an endoenergetic process of
electron removal.
Note that instead of the 6311G(2df,2pd) basis, we could have used another
triplezeta quality basis containing polarization functions, e.g., the
correlationconsistent ccpVTZ basis. These bases ensure results close to the
basisset limit for VIPs
[].
 