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Transcript
special topic in physics AP4174 an introduction to electronic orbital theory The specific goals of the course are: •to analyze the nature and behaviour of electronic orbitals •to show how we can use the characteristics of orbitals in order to: – make a material more stable in energy – change the binding between atoms to modify the structural, physical and chemical properties of materials to achieve desired results 1 The following questions will be treated: • What can we learn about the stability and properties of a material by analyzing its electronic orbitals? Such knowledge will allow more powerful prediction. What was known before? • Why is it necessary to consider quantum mechanics? Why does classical mechanics fail? • What is an electronic orbital? • What are the nature and behaviour of molecular orbitals? How can we build them from simple “intuition” and symmetry? How can we build molecular orbitals with elementary methods (such as the Huckel approach)? • Which information do the electronic orbitals provide? • How can we manipulate the electronic orbitals? A brief introduction to the versatile perturbation theory. • How can we achieve greater precision when needed? A brief 2 introduction to more accurate calculations. Representation and modeling of Molecules This is an introductory course to present both the traditional representations of the molecules and the concepts behind an initiation to quantum mechanics and to orbital theory No mathematical pre-requisite is necessary. The first part is for beginners in chemistry or physicist not familiar with chemical language. The second part of the course will first justify why QM approach is necessary at the atomic level, next briefly introduce operators and wave functions and finally shows that simple approaches are affordable an only use well known comprehensive tools. With the progression of the course, the mathematics will progressively disappear in favor of pictorial and qualitative descriptions. Manipulating orbitals, a qualitative view of orbitals. This is an introductive course on Molecular Orbital theory and modeling. The emphasis is made on concepts such as symmetry preservation and not in calculations. Introduction to calculations methods will focus on the input-outputs and on their validity domain (How to choose them? How to use them? What are the limitations?). The MO theory is applied to prediction and analysis of structures and reactivity. The courses of the two semesters are independent even though it is better to take them successively. 3 AP4273-AP8273 an introduction to electronic orbital theory 4 AP4273-AP8273 an introduction to electronic orbital theory, Counting electrons Lewis structure SO32- Molecular orbital CCl4 Atomic orbitals 5 Different ways of counting and representing electrons Planar representation Lewis structure SO32- * * * ** Spatial Representation VSEPR 6 How to guess a geometry? Search for total energy minimum Improve stability of orbitals Orbital of H2O 1b2 favors linearity and 1a1 bending 7 Butadiene -.3717 LCAO MOs are made of AOs -.6015 -1.618 0.3717 0.6015 2 different phases 0.6015 -.3717 -.618 0.6015 -.3717 -.6015 0.3717 0.618 -.3717 0.6015 0.6015 1.618 0.6015 0.3717 8 Butadiene -.3717 What can we learn ? -.6015 An electronic description 0.3717 (measure the bond strengths And delocalisation) Information on structure (avoid connecting the “ends”) 0.6015 Information on reactivity (react from both ends… More … -1.618 0.6015 0.6015 -.3717 -.618 -.3717 -.6015 0.3717 0.618 -.3717 0.6015 0.6015 1.618 0.6015 0.3717 9 The “conservation of the HOMO” hn D 10 HF The orbital approximation consists to treat the electrons as independent. Electrons are not independent. HF preserves the orbital “independency” by taking as orbital that consistent with the average distribution of the others. This method is iterative (self consistent) and satisfies the Pauli principle. 11 11 Electronic correlation Correlation requires to take into account the relative positions of the electron that are quite never the average place. • VB method and polyelectronic functions • IC (beyond HF) • DFT 12 Skip! Sleep if you want! 13 For clarity, simple structures will be used to illustrate the concepts and methods of this course. An introduction to calculations for larger structures (including periodic crystals) and a presentation of codes are planned to conclude this course. There are no pre-requisites to enroll in this course. An active participation by the students is expected. 14 Christian MINOT G6620 [email protected] Flexibility (lecture and tutorial), please let me know how to adapt. Code demonstrations Controls of knowledge. Questions? 15