Quantum chemistry establishment

Theoretical Quantum Chemistry Establishing a New Science in the Twentieth Century... 

It should also be acknowledged that in recent years computational quantum chemistry has achieved a number of predictions that have since been experimentelly confirmed (45-47). On the other hand, since numerous anomalies remain even within attempts to explain the properties of atoms in terms of quantum mechanics, the field of molecular quantum mechanics can hardly be regarded as resting on a firm foundation (48). Also, as many authors have pointed out, the vast majority of ab initio research judges its methods merely by comparison with experimental date and does not seek to establish internal criteria to predict error bounds theoretically (49-51). The message to chemical education must, therefore, be not to emphasize the power of quantum mechanics in chemistry and not to imply that it necessarily holds the final answers to difficult chemical questions (52). 

Formal structures for the acquisition of academic degrees in quantum chemistry were established in the year following Lowdin s appointment to the chair in May 1960. Anders Froman became the first to earn the fil. lie. degree in December 1961 and thus started the "institutionalization" of the field. It had until then a flavor of novelty and exclusivity which was embraced by some and repelled others. The new status changed the prerequisites for graduate studies as well, undergraduate chemistry as well as experimental physics should now be a part of the baggage of new students. 

Per-Olov Lowdin established both the Quantum Chemistry Group at Uppsala and the Quantum Theory Project at Gainesville through his personal and scientific stature and he was unquestionably the Director of both operations. Several prominent scientists were invited during the first years to be Associate Directors and to maintain the spirit when "the Force" was absent. Yngve Ohrn was invited to join the faculty at Florida as Associate Professor in 1966 and he chose to become a member of the Quantum Theory Project. He assumed the Associate Directorship of the Quantum Theory Project in 1967 and proved quickly to have the qualities that allowed him to deal effectively with the university administration at all levels as well as with issues within the rather diverse and extensive body of scientists and students of the Project. Fairness, compassion, and persistence are words that come to my mind when I characterize Yngve s leadership. 

The successful chairmanship and the apparent qualities of personnel management landed several offers of deanships in Yngve s lap. He decided, to my delight, to remain a dedicated scientist. Administrative obligations remained, he assumed the role of Director of the Quantum Theory Project in 1983 and led this rather informal association of faculty members from Chemistry and Physics to be established, in 1987, as the "Institute for Theory and Computation in Molecular and Materials Sciences" with a well defined position in the University system. This was another demonstration of the ability to create coherence and commitment amongst a body of strong minded people with diverse interests. It is a consequence that Florida remains a world renowned hub of quantum chemistry activities. 

The first study in which a full CASSCF treatment was used for the non-adiabatic dynamics of a polyatomic system was a study on a model of the retinal chromophore [86]. The cis-trans photoisomerization of retinal is the primary event in vision, but despite much study the mechanism for this process is still unclear. The minimal model for retinal is 2-cis-C5H6NH2, which had been studied in an earlier quantum chemistry study [230]. There, it had been established that a conical intersection exists between the Si and So states with the cis-trans defining torsion angle at approximately a = 80° (cis is at 0°). Two... 

Since the early days of quantum mechanics, the wave function theory has proven to be very successful in describing many different quantum processes and phenomena. However, in many problems of quantum chemistry and solid-state physics, where the dimensionality of the systems studied is relatively high, ab initio calculations of the structure of atoms, molecules, clusters, and crystals, and their interactions are very often prohibitive. Hence, alternative formulations based on the direct use of the probability density, gathered under what is generally known as the density matrix theory [1], were also developed since the very beginning of the new mechanics. The independent electron approximation or Thomas-Fermi model, and the Hartree and Hartree-Fock approaches are former statistical models developed in that direction [2]. These models can be considered direct predecessors of the more recent density functional theory (DFT) [3], whose principles were established by Hohenberg,... 

What was the distinction between quantum chemistry and chemical physics After the Journal of Chemical Physics was established, it was easy to say that chemical physics was anything found in the new journal. This included molecular spectroscopy and molecular structures, the quantum mechanical treatment of electronic structure of molecules and crystals and the problem of chemical binding, the kinetics of chemical reactions from the standpoint of basic physical principles, the thermodynamic properties of substances and calculation by statistical mechanical methods, the structure of crystals, and surface phenomena. 

Quantum chemists, like chemical physicists, tended to characterize their field as one in which the distinction between theoreticians and experimentalists is not so sharp. 120 They prided themselves on intellectual flexibility, and they frequently exhibited social flexibility. Perhaps for these very reasons quantum chemistry was able to establish a special niche in the United States in the 1930s, when the departmental structures of American universities were permeable and personal fiefdoms fairly rare. 

Take an N-atomic molecule with the nuclei each at their equilibrium internuclear position. Establish a Cartesian x, y, z coordinate system for each of the nuclei such that, for Xj with i = 1,.., 3N, xi is the Cartesian x displacement of nucleus 1, x2 is the Cartesian y displacement coordinate for nucleus 1, X3 is the Cartesian z displacement coordinate for nucleus 1,..., x3N is the Cartesian z displacement for nucleus N. Use of one or another quantum chemistry program yields a set of force constants I ij in Cartesian displacement coordinates... 

Because the energy of the activated complex is higher than the energies of reactants and of the final reaction products, it is crucial to establish how many activated complexes may form at given P-T-X conditions. This can be done by application of quantum chemistry concepts. 

It is instructive, however, in order to establish the connection between the usual methods in quantum chemistry - based on molecular orbitals - and the local-scaling transformation version of density functional theory, to discuss Cioslowski s work in some detail. 

We propose [15] a set of basis tensor algebra subroutines or btas. Tensors and tensor operators arise in many fields in the computational sciences, including computational quantum chemistry. The nomenclature BTAs(m,n), with m > n, where m and n are the respective ranks of the tensors, is proposed to establish a high level classification of tensor operations. The BTAS can be classified as follows -BTAS(1,0) BTAS(1,1)... 

The establishment of the reduction of one scientific discipline to another one by philosophers of science requires more than an appeal to the importance of DNA in biology or success of quantum chemistry. It requires that formal relations be established between the two fields in question. At least this has been... 

Since uracil and thymine, like cytosine, are fundamental nucleic acid bases, they have been treated by many methods of quantum chemistry in view to establish the essential electronic characteristics of their ground states. 

The numerical solution of large matrix eigenvalue problems is one of the most frequently encountered computation tasks of a standard, yet nontrivial nature. Consequently, there is great theoretical and practical interest in the invention, modification and assessment of methods to cope with this problem. This chapter will describe some well-established methods, currently of widespread use in quantum-chemistry programs. 

It is clear that the various density functional schemes for molecular applications rely on physical aiguments pertaining to specific systems, such as an electron gas, and fitting of parameters to produce eneigy functionals, which are certainly not universal. By focusing on the energy functional one has given up the connection to established quantum mechanics, which employs Hamiltonians and Hilbert spaces. One has then also abandoned the tradition of quantum chemistry of the development of hierarchies of approximations, which allows for step-wise systematic improvements of the description of electronic properties. 

The subject of Quantum Chemistry is today represented at every major University and the activities mentioned above have resulted in strong international and global networks thanks to the leadership of Per-Olov Lowdin. Through outstanding activities during his lifetime he has influenced generations of physicists and chemists and established important links between the fields of physics, chemistry and biology. 

Quantum chemistry is the foundation of molecular chemistry dealing with structure, properties, and interaction of molecules. The basic principles are offered by quantum mechanics. Quantum-chemical calculations are able to supply information needed for molecular descriptors for QSAR analyses. The use of quantum-chemical calculations is becoming common to establish molecular equilibrium geometries and conformations and to supply quantitative thermochemical and kinetic data. 

The fourth symposium, organized by Gulzari Malli (Simon Fraser University) and Bob Snider (University of British Columbia) was held in 1971 on UBC s beautiful campus in Vancouver. Plans for the fifth symposium in the nation s capital, Ottawa, were modified when the First International Congress of Quantum Chemistry was organized in 1973 in Menton, France. David Bishop (University of Ottawa) and Vedene Smith (Queen s University) organized the fifth symposium in Ottawa in 1974. The shift from a biennial to a triennial conference established a natural rotation between the American Conference on Theoretical Chemistry,18 the Canadian Symposium on Theoretical Chemistry, and the International Congress of Quantum Chemistry. This rotation has continued without interruption for more than two decades. 

Karachalios chapter shows the fine structure and the local character of knowledge production as well as its dependence on information exchange, and the same can be said of the contribution from Blondel-Megrelis. The career of Jean Barriol after the war and the establishment of the Theoretical Chemistry Laboratory at Nancy extends the story to the period after World War II and expands it to include France. As with Bonino, Barriol regarded the interplay of theory and experiment as of utmost importance for a fruitful development of theoretical chemistry. Although after 1945 the scientific contacts of France with its allies were quite strong, illustrated by the fact that the first conference on quantum chemistry after the war was held in Paris in 1948, the establishment of Barriol s laboratory was closely connected to French... 

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