Conceptual Quantum Chemistry

M. Quack and M. A. Suhm, Potential energy hypersurfaces for hydrogen bonded clusters (HF) , in Conceptual Perspectives in Quantum Chemistry, Conceptual Trends in Quantum Chemistry, Vol. Ill, J. L. Calais and E. S. Kryachko, ed., Kluwer, Dordrecht, 1997, pp. 415 463. 

This line of research has not lost his momentum. One of the reasons is the eontinuing progress in the computer hardware and software. Methods and algorithms are, and will be, continuously updated to exploit new features made available by eomputer seienee, as for example the parallel architectures, or the neuronal networks, to mention things at present of widespread interest, or even conceptually less significant improvements, as the inerease of fast memory in commereial computers. Computer quantum chemistry is not a mere recipient of progresses in eomputer seienee. Many progresses in the software comes from... 

Summing up, we may say that approximation methods in quantum chemistry generally involve (either explicitly or implicitly) a model H(i)> and associated model chemistry that more or less mimics the true behavior of Eq. (1.1). Such models might be closely patterned after the well-known conceptual models of empirical... 

We turn now in the next several chapters to specific aspects of the working out of the fundamental organizational and conceptual principles defining chemistry in the nineteeth century. We then turn to the development of new specializations as a result of the work of distinctive research schools, in particular, the formation of the disciplines, or subfields, of physical chemistry, physical organic chemistry, and quantum chemistry. Together these new disciplines achieved the status and the goals of those eighteenth-century chemical philosophers who had dreamed of a true "theoretical chemistry."... 

Avery, J., in Conceptual Trends in Quantum Chemistry, E.S. Kryachko and J.L. Calais (eds.), Kluwer Academic Publishers, Dordrecht, Netherlands, (1994), pp. 135-169. 

Then, we focused on conceptual problems such as the definition of local spins that do hardly emerge naturally in holistic quantum theory. The local spin concept was rigorously introduced in quantum chemistry about 10 years ago by Clark and Davidson. We reviewed the most important contributions in this field and... 

On the other hand, significant advances have also been made in the broader domain of quantum chemistry, a prime example being areas of research that involve the continuous spectrum and, as such, are more complex, conceptually, formally, and computationally. When the continuous spectrum of a quantum system acquires physical significance, a plethora of special and challenging physical and mathematical features and questions emerge that are absent in problems involving just the discrete spectrum. 

We hope the reader has been convinced that it is technically feasible to describe a photochemical reaction coordinate, from energy absorption to photoproduct formation, by means of methods that are available in standard quantum chemistry packages such as Gaussian (e.g., OPT = Conical). The conceptual problems that need to be understood in order to apply quantum chemistry to photochemistry problems relate mainly to the characterization of the conical intersection funnel. We hope that the theoretical discussion of these problems and the examples given in the last section can provide the information necessary for the reader to attempt such computations. 

J.V. Ortiz et al., in One-Electron Pictures of Electronic Structure Propagator Calculations on Photoelectron Spectra of Aromatic Molecules, ed. by J.-L. Calais, E. Kryachko Conceptual Perspectives in Quantum Chemistry, Vol. 3 (Kluwer, Dordrecht, 1997), pp. 465-517... 

The problem with the conceptually simple form of the KS equations is the choice of the functionals which determine the operator FKS in equations 3. While the HF operator F is known but yields only approximate energies, the operator FKS gives the correct energy but the functional is not known. The form of FKS can only be guessed The popularity of DFT in molecular quantum chemistry which came in the last decade is because the guesses have been very successful. New types of functionals have been suggested for Fks which yield a much higher accuracy than earlier functionals. 

Jean-Louis Calais and Eugene Kryachko, Conceptual Perspectives in Quantum Chemistry, Kluwer, Dordrecht, 1997. 

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