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20_01fig_PChem.jpg Hydrogen Atom M m r Potential Energy + Kinetic Energy R C

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20_01fig_PChem.jpg Hydrogen Atom RadialAngular Coulombic

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20_01fig_PChem.jpg Hydrogen Atom will be an eigenfunction of Separable

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20_01fig_PChem.jpg Hydrogen Atom Recall Bohr Radius

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20_01fig_PChem.jpg Hydrogen Atom Assume Let’s try It is a ground state as it has no nodes

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20_01fig_PChem.jpg Hydrogen Atom The ground state as it has no nodes n=1, and since l =0 and m = 0, the wavefunction will have no angular dependence

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20_01fig_PChem.jpg Hydrogen Atom In general: Laguerre Polynomials 1S- 0 nodes 2S- 1 node 3S-2 nodes

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Energies of the Hydrogen Atom In general: Hartrees kJ/mol

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Wave functions of the Hydrogen Atom In general: Z=1, n = 1, l = 0, and m = 0:

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Z=1, n = 2, l = 0, and m = 0: Wave functions of the Hydrogen Atom

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Hydrogen Atom Z=1, n = 2, l = 1 m = 0:m = +1/-1: + _

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20_06fig_PChem.jpg For radial distribution functions we integrate over all angles only Prob. density as a function of r. Radial Distribution Functions

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20_09fig_PChem.jpg Radial Distribution Functions

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20_08fig_PChem.jpg X Y Z Probability Distributions

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20_12fig_PChem.jpg Atomic Units Set: Hartrees a.u. Much simpler forms.

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Atoms Potential Energy Kinetic Energy C meme meme =r 12 M

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Helium Atom C meme meme =r 12 M Cannot be separated!!! Hydrogen like 1 e’ Hamiltonian i.e. r 12 cannot be expressed as a function of just r 1 or just r 2 What kind of approximations can be made?

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Ground State Energy of Helium Atom EoEo E1E1 E2E2 I 1 = ev EoEo E1E1 E2E2 I 2 = ev Ionization Energy of He E Free E o = ev = ev = Hartrees Perturbation Theory

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Ground State Energy of Helium Atom H Not even close. Off by 1.1 H, or 3000 kJ/mol Therefore e’-e’ correlation, V ee, is very significant

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Ground State Energy of Helium Atom

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Closer but still far off!!! Perturbation is too large for PT to be accurate, much higher corrections would be required

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Variational Method The wavefunction can be optimized to the system to make it more suitable Consider a trail wavefunction and Is the true wavefunction, where: Then The exact energy is a lower bound is a complete set Assume the trial function can be expressed in terms of the exact functions We need to show that

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Variational Method Since Variational Energy E0E0 E var ( ) min

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Variational Method For He Atom Let’s optimize the value of Z, since the presence of a second electrons shields the nucleus, effectively lowering its charge.

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Variational Method For He Atom

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Similarly Recall from PT

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Variational Method For He Atom Much closer to H ( E= H = kJ/mol error)

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Variational Method For He Atom Optimized wavefunction

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Variational Method For He Atom Optimized wavefunction Other Trail Functions ( E= H = kJ/mol error) Optimizes both nuclear charges simultaneously

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Variational Method For He Atom Other Trail Functions ( E= H = kJ/mol error) Z’, b are optimized. Accounts for dependence on r 12. In M.O. calculations the wavefunction used are designed to give the most accurate energies for the least computational effort required. The more accurate the energy the more parameters that must be optimized the more demanding the calculation.

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Variational Method For He Atom In M.O. calculations the wavefunction used are designed to give the most accurate energies for the least computational effort required. The more accurate the energy the more parameters that must be optimized the more demanding the calculation H H H Experimental ev H

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