Electron correlation history

We want to stress that the present article is not intended to present the history of or to give a detailed account of concepts such as pairing and gap equations. Our aim is only to stress that such concepts, which have already been so useful in nuclear physics and certain parts of solid-state physics, should be further exploited for the study of electronic correlation in extended systems. 

Looking at the history of correlation from the fifties to the seventies, one may be led to ask whether correlation has been a scientific fashion or a real problem. Twenty years ago, almost everybody seemed to accept the idea that the simple molecular orbital method (MO) must be completed by configuration interaction (Cl), in order to obtain reliable prediction for the physical properties of atoms and molecules. Ten years ago, electron correlation was considered as the central problem of Quantum Chemistry (7). Nowadays, about 90% of the quantum-mechanical calculations on molecules are performed by the self-consistent-field method (SCF) using more or less extended sets of basis functions, without any consideration of the possible effects of correlation. 

The history and the present state of the treatment of electron correlation is reviewed. For very small atoms or molecules calculations of higher than spectroscopic accuracy are possible. A detailed account for many-electron methods in terms of one-electron basis sets is given with particular attention to the scaling of computer requirements with the size of the molecule. The problems related to the correlation cusp, especially the slow convergence of a basis expansion, as well as their solutions are discussed. The unphysical scaling with the particle number may be overcome by localized-correlation methods. Finally density functional methods as an alternative to traditional ab-initio methods are reviewed. 

Keywords Computational chemistry history Isaiah Shavitt Configuration interaction Electron correlation Graphical Unitary Group Approach COLUMBUS Programs... 

If multiple bonding is present, then we can expect to see significant structural changes as we improve the level of theory to take electron correlation into account. Take rC—C in benzene. HF/6-31G returns a value of 1.386 A switching to MP2 or B3LYP increases the distance to 1.397 A, an exact match with the value obtained experimentally by gas electron diffraction. A similar problem exists if lone pairs are present on neighboring atoms the structure of N2O3, the subject of one of our case histories (Section 12.3), is problematic to calculate for this reason. 

Also, the increasing application of alumina films in the electronics industry requires that attention be paid to their electrophysical properties (dielectric strength, conduction, etc.). However, since the work of Goruk, Young, and Zobel,5 published as long ago as 1966 in this same series, no articles reviewing these problems have appeared. An attempt is made here to emphasize the correlation between the electrophysical properties of oxides and the history of their growth. 

There has been a long history of attempts to correlate electronic excitation energies with one-particle energies. In particular one can derive theoretical expressions (12, 13)... 

Since the strength of adsorption depends on surface electronic interactions between adsorbent and catalyst, a correlation of reaction rate and d-band character of simple metals is expected [Fig. 9 (772)] similar to gas phase catalysis (23, 24). The correlation seems to fail within the noble metal group, and this may result from the existence of multiple adsorption states and the structure, history, and activity of the catalysts used. 

The DFT method has a long history behind it, which began with Thomas, Dirac, Fermi, etc. At the beginning, the successes were quite modest (the electron gas dieory, known as the Xa method). Real success came after a publication by Jan Andzehn and Ericb Wimmer. The DFT method, offering results at a correlated level for a wide spectrum of physical quantities, turned out to be roughly as inexpensive as the Hartree-Fock proceduie-this is the most sensational feature of the method. 

---