Accurate electronic
structure computations
One of the key
questions in electronic structure theory concerns the accuracy of the computed
molecular quantities, including relative energies. The composite focal-point
analysis (FPA) approach developed some two decades ago by us provides a clean
way to determine the uncertainties of computed relative energies.
Related publications:
W.
D. Allen, A. L. L. East, and A. G. Császár, Structures and Conformations of
Non-Rigid Molecules, edited by J. Laane, M. Dakkouri, B. van der Veken and H.
Oberhammer (Kluwer, Dordrecht, 1993), pp. 343-373.
A.
G. Császár, W. D. Allen, and H. F. Schaefer, III, In Pursuit of the Ab Initio
Limit for Conformational Energy Prototypes, J.
Chem. Phys. 1998, 108,
9751-9764.
A.
G. Császár, W. D. Allen, Y.
Yamaguchi, and H. F. Schaefer III, Ab
Initio Determination of Accurate Potential Energy Hypersurfaces for the
Ground Electronic States of Molecules, in Computational
Molecular Spectroscopy, 2000,
eds. P. Jensen and P. R. Bunker, Wiley: New York.
A.
G. Császár, G. Tarczay, M.
L. Leininger, O. L. Polyansky, J. Tennyson, and W. D. Allen, Dream or Reality:
Complete Basis Set Full Configuration Interaction Potential Energy
Hypersurfaces, in Spectroscopy from Space,
edited by J. Demaison, K. Sarka, and E. A. Cohen (Kluwer, Dordrecht, 2001),
pp. 317-339.
NEAT: From a Network of Computed Reaction Enthalpies
to Atom-Based Thermochemistry
NEAT is a simple and fast, weighted, linear
least-squares refinement protocol and code for inverting the information
contained in a network of quantum chemically computed 0 K reaction enthalpies.
This inversion yields internally consistent 0 K enthalpies of formation for the
species of the network. The refinement takes advantage of the fact that the
accuracy of computed enthalpies depends strongly on the quantum-chemical
protocol employed for their determination. Different protocols suffer from
different sources of error; thus, the reaction enthalpies computed by them have
“random” residual errors. Since it is much more natural for quantum-chemical
energy and enthalpy results, including reaction enthalpies, to be based on the
electronic ground states of the atoms and not on the historically preferred
elemental states, and since these two possible protocols can be converted into
each other straightforwardly, it is proposed that first-principles
thermochemistry should employ the ground electronic states of atoms. In this
scheme, called atom-based thermochemistry (AT), the enthalpy of formation of a
gaseous compound corresponds simply to the total atomization energy of the
species; it is always positive, and it reflects the bonding strength within the
molecule. The inversion protocol developed and based on AT is termed NEAT,
which represents the fact that the protocol proceeds from a network of computed
reaction enthalpies toward atom-based thermochemistry, most directly to
atom-based enthalpies of formation.
Related publications:
A. G. Császár and
T. Furtenbacher, From a Network of Computed Reaction Enthalpies to Atom-Based
Thermochemistry (NEAT), Chem. Eur. J.
2010, 16(16), 4826-4835.