Handbook or Computational Chemistry
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Handbook or Computational Chemistry
Jerzy LeszczynskiEditorSPRINGERAnna Kaczmarek-Kẹdziera REFERENCEManthos G. PapadopoulosHeribert ReisAndrzej J. SadlejManoj K. ShuklaCo-EditorsHandbook Handbook or Computational Chemistry k ofComputational Chemistry0 springer1 From Quantum Theory to Computational Chemistry. A Brief Account of DevelopmentsLucjan PielaDepartment of Chemistry, University of Warsaw, PolandIntroduction - Exceptional Status of Chemistry....................2A Hypothetical Perfect Computer................... Handbook or Computational Chemistry ................5Does Predicting Mean Understanding?...............................7Orbital Model.....................................................Handbook or Computational Chemistry
9Power of Computer Experiments....................................10Conclusions......................................................10AcknowledgmentsJerzy LeszczynskiEditorSPRINGERAnna Kaczmarek-Kẹdziera REFERENCEManthos G. PapadopoulosHeribert ReisAndrzej J. SadlejManoj K. ShuklaCo-EditorsHandbook Handbook or Computational Chemistry tional Chemistry. A Brief Account of DevelopmentsAbstract: Quantum chemical calculations rely on a few fortunate circumstances, like usually small relativistic and negligible electrodynamic (QED) corrections, and large nuclei-to-electrons mass ratio. Unprecedented progress in computer technology has Handbook or Computational Chemistry revolutionized quantum chemistry, making it a valuable tool for experimenters. It is important for computational chemistry to elaborate methods thatHandbook or Computational Chemistry
look at molecules in a multiscale way, provide its global and synthetic description, and compare this description with those for other molecules. OnlyJerzy LeszczynskiEditorSPRINGERAnna Kaczmarek-Kẹdziera REFERENCEManthos G. PapadopoulosHeribert ReisAndrzej J. SadlejManoj K. ShuklaCo-EditorsHandbook Handbook or Computational Chemistry and computational chemistry should provide the tools for seeing this.Introduction - Exceptional Status of ChemistryContemporary science fails to explain the largest-scale phenomena taking place in the universe, such as the speeding up of the galaxies (supposedly due to the undefined “black energy”) Handbook or Computational Chemistry and the nature of the lion’s share of the universe’s matter (and also unknown “dark matter”).Quantum chemistry is in a far better position, which mayHandbook or Computational Chemistry
be regarded even as exceptional in the sciences. The chemical phenomena are explainable down to individual molecules (which represent the subject of qJerzy LeszczynskiEditorSPRINGERAnna Kaczmarek-Kẹdziera REFERENCEManthos G. PapadopoulosHeribert ReisAndrzej J. SadlejManoj K. ShuklaCo-EditorsHandbook Handbook or Computational Chemistry 926a, b, c, d) offers in most cases a quantitatively correct picture. Only molecules with very heavy atoms, due to the relativistic effects becoming important, need to be treated in a special way based on the Dirac theory (Dirac 1928a, b). Ulis involves an approximate Hamiltonian in the form of the Handbook or Computational Chemistry sum of Dirac Hamiltonians for individual electrons, and the electron-electron interactions in the form of the (non-relativistic) Coulomb terms, a commHandbook or Computational Chemistry
on and computationally successful practice ignoring, however, the resulting resonance character of all the eigenvalues (Brown and Ravenhall 1951; PestJerzy LeszczynskiEditorSPRINGERAnna Kaczmarek-Kẹdziera REFERENCEManthos G. PapadopoulosHeribert ReisAndrzej J. SadlejManoj K. ShuklaCo-EditorsHandbook Handbook or Computational Chemistry urrently far from routine application, but still feasible for very small systems (Lach et al. 2004).This success of computational quantum chemistry is based on a few quite fortunate circumstances (for references see, e.g., Piela 2007):•Atoms and molecules are built of only two kinds of particles: nu Handbook or Computational Chemistry clei and electrons.•Although nuclei have non-zero size (electrons are regarded as point-like particles), the size is so small that its influence is beHandbook or Computational Chemistry
low chemical accuracy (Lach et al. 2004). Therefore, all the constituents of atoms and molecules are treated routinely as point charges.•Hie QED correJerzy LeszczynskiEditorSPRINGERAnna Kaczmarek-Kẹdziera REFERENCEManthos G. PapadopoulosHeribert ReisAndrzej J. SadlejManoj K. ShuklaCo-EditorsHandbook Handbook or Computational Chemistry 04).•The nuclei are thousands times heavier than electrons and therefore, except in some special situations, they move thousands times slower than electrons. This makes it possible to solve the Schrodinger equation for electrons, assuming that the nuclei do not move, i.e., their positions are fixed Handbook or Computational Chemistry in space (“clamped nuclei”). This concept is usually presented within the so called adiabatic approximation. In this approximation the motion of the nHandbook or Computational Chemistry
uclei is considered in the next step, in which the electronic energy (precalculated for any position of the nuclei), together with a usually small diaJerzy LeszczynskiEditorSPRINGERAnna Kaczmarek-Kẹdziera REFERENCEManthos G. PapadopoulosHeribert ReisAndrzej J. SadlejManoj K. ShuklaCo-EditorsHandbook Handbook or Computational Chemistry Computational Chemistry. A Brief Account of Developments3function is assumed to be a product of the electronic wave function and of the function describing the motion of the nuclei. The commonly used Born-Oppenheimer (Born and Oppenheimer 1927) approximation (B-0) is less accurate than the adiabatic Handbook or Computational Chemistry one, because it neglects the above-mentioned diagonal correction, making the PES independent of nuclear masses. Using the PES concept one may introduHandbook or Computational Chemistry
ce the crucial idea of the spatial structure of a molecule, defined as those positions of the nuclei that assure a minimum of the PES. This concept maJerzy LeszczynskiEditorSPRINGERAnna Kaczmarek-Kẹdziera REFERENCEManthos G. PapadopoulosHeribert ReisAndrzej J. SadlejManoj K. ShuklaCo-EditorsHandbook Handbook or Computational Chemistry mic cores, atom-atom bonds, and atomic lone pairs.Jerzy LeszczynskiEditorSPRINGERAnna Kaczmarek-Kẹdziera REFERENCEManthos G. PapadopoulosHeribert ReisAndrzej J. SadlejManoj K. ShuklaCo-EditorsHandbookGọi ngay
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