Notes from the Gaussian Users' Meeting

The day before the start of Pacifichem (December 14), an all-day Gaussian Users' Meeting was held in Honolulu. Mike Frisch provided a brief introduction. Gary Trucks gave a comprehensive analysis of the performance of several DFT functionals. In his experience, of the pure functionals, HCTH is the best for geometries; while O3LYP is the best among the hybrid functionals (X3LYP is really no improvement over B3LYP, although it was designed to be). MP2 has problems; for instance, it predicts that the ground state of benzene is non-planar! For frequencies, HCTH and tauHCTH are the best pure functionals, while O3LYP and tauHCTH are the best hybrid functionals -- errors vary systematically. Again X3LYP is no improvement over B3LYP. Thus the best choice for geometry andfrequency is O3LYP, with HCTH second. Overall BMK is bad; it sacrifices geometries and frequencies. B3P86, PBE/PBE and B3LYP are good general purpose functionals. For electronic excitations, B3P86 is the best general purpose functional, PBE/PBE is sometimes ok. Overall B3P86 is comparable to anything in the last 15 years. Overall, O3LYP is good for geometries and frequencies; HCTH is the best pure functional. B3P86 is better if electronic excitations are important.

The next talk was on PCModel: Saunders, Houk, Wu, Still, Lipton, Cheng & Guida, JACS 112, 1419-1427 (1990). Grid methods suffer from combinatorial explosion, but guarantee a solution. Stochastic methods, on the other hand, give up the guarantee of a solution in favour of speed.

• Cartesian search works well if lots of rings and constraints; searches local space well;
• Dihedral search works better on long, staurated chains; searches global space.

Rina Dukor (BioTools) then spoke on Chiro-optic properties. She pointed out that 9 of the top-10 drugs have chiral active ingredients. e.g.:

• Warfarin -- both enantiomers are anticoagulants;
• Propanolol -- S enantiomer is a beta-blocker, R is not;
• Sotalol -- enantiomers have different activities;
• Leva Dopa -- one enantiomer is a drug, another is toxic!

IR spectra of enantiomers are identical, but their VCD spectra are opposite in sign; CD is the difference in absorbance of left - right circularly polarized light. VCD is an alternate to XRD for determination of absolute conformation. g03 can now compute VCD, CD (electronic), ROA, ORD. A free online database and searchable (by CAS#) literature on VCD spectra can be found on btools.com

Bernie Schlegel spoke on AIMD. BOMD converges the wavefunction at each step and propagate the nuclei. Car-Parinello propagates the wavefunction along with geometry using an extended Lagrangian. Ehrenfest method propagates the wavefunction using TD HF/DFT and propagates the nuclei using classical trajectories. In CP:

• orbitals are expanded in plane waves,
• plane wave coefficients being propagated with an extended Lagrangian;
• FFT is used for propagation;
• gradients require only Hellmann-Feynman terms.

In ADMP (Atom-centered Density Matrix Propagation):

• orbitals are expanded in atom-centered basis,
• far wewer basis basis functions being needed than plane waves;
• Density Matrix propagation using an extended Lagrangian;
• FFT is used for propagation;
• gradients require Hellmann-Feynman and Pulay terms.

Euler-Lagrange equations of motion used for nuclei and for Density Matrix (with a fictitious mass for components of the Density Matrix); integrate using velocity Verlet algorithm.

The last speaker was Doug Fox, who gave us the fruits of his years of experience on Geometry Optimization. Cartesians or Z-matrix, either can be used to set up the initial state:

• Opt=Z-matrix or Opt=ModRedundant;
• Opt=(TS,CalcFC) for TS Search works if you can start from a good geometry;
• Opt=(QST2/3) helps bracket the search region;
• Opt=(QST2,Path=n) is useful if you also want to map the path.
• Opt=ModRedundant needs input for each structure (or a blank line).

Order of structures: Reactants, Products, TS for QST3
Beware order mismatch for atoms in TS Search! Use GaussView -> Atom Editor -> Connection Editor -> AutoFix
Symmetry is normally handled by inputing coordinates in the right symmetry. This is a good use of Z-matrix, e.g. for getting angles right.
Wrong # negative eigenvalues =>

• TS Search with 2 or 0 negative eigenvalues;
• or Minimum with 1 or more negative eigenvalues.

Wrong chemistry => TS which connects different chemistries.
GaussView can be helpful to follow a failed optimization. Check the progress of optimization using Eigenvector Following. The meeting concluded with a brief panel discussion.