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P460 - 3D S.E.1 3D Schrodinger Equation Simply substitute momentum operator do particle in box and H atom added dimensions give more quantum numbers. Can.

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Presentation on theme: "P460 - 3D S.E.1 3D Schrodinger Equation Simply substitute momentum operator do particle in box and H atom added dimensions give more quantum numbers. Can."— Presentation transcript:

1 P460 - 3D S.E.1 3D Schrodinger Equation Simply substitute momentum operator do particle in box and H atom added dimensions give more quantum numbers. Can have degeneracies (more than 1 state with same energy). Added complexity. Solve by separating variables

2 P460 - 3D S.E.2 If V well-behaved can separate further: V(r) or V x (x)+V y (y)+V z (z). Looking at second one: LHS depends on x,y RHS depends on z S = separation constant. Repeat for x and y

3 P460 - 3D S.E.3 Example: 2D (~same as 3D) particle in a Square Box solve 2 differential equations and get symmetry as square. “broken” if rectangle

4 P460 - 3D S.E.4 2D gives 2 quantum numbers. Level nx ny Energy 1-1 1 1 2E0 1-2 1 2 5E0 2-1 2 1 5E0 2-2 2 2 8E0

5 P460 - 3D S.E.5 for degenerate levels, wave functions can mix (unless “something” breaks degeneracy: external or internal B/E field, deformation….) this still satisfies S.E. with E=5E0

6 P460 - 3D S.E.6 Spherical Coordinates Can solve S.E. if V(r) function only of radial coordinate volume element is

7 P460 - 3D S.E.7 Spherical Coordinates solve by separation of variables multiply each side by

8 P460 - 3D S.E.8 Spherical Coordinates-Phi Look at phi equation first. Have separation constant constant (knowing answer allows form) must be single valued the theta equation will add a constraint on the m quantum number

9 P460 - 3D S.E.9 Spherical Coordinates-Theta Take phi equation, plug into (theta,r) and rearrange. Have second separation constant knowing answer gives form of constant. Gives theta equation which depends on 2 quantum numbers.

10 P460 - 3D S.E.10 Spherical Coordinates-Theta Associated Legendre equation. Can use either analytical (calculus) or algebraic (group theory) to solve. Do analytical. Start with Legendre equation

11 P460 - 3D S.E.11 Spherical Coordinates-Theta Get associated Legendre functions by taking the derivative of the Legendre function. Prove by substitution into Legendre equation Note that power of P determines how many derivatives one can do. Solve Legendre equation by series solution

12 P460 - 3D S.E.12 Solving Legendre Equation Plug series terms into Legendre equation let k=j+2 in first part and k=j in second (think of it as having two independent sums). Combine all terms with same power gives recursion relationship series ends if a value equals 0  L=j=integer end up with odd/even (Parity) series

13 P460 - 3D S.E.13 Solving Legendre Equation Can start making Legendre polynomials. Be in ascending power order can now form associated Legendre polynomials. Can only have l derivatives of each Legendre polynomial. Gives constraint on m (theta solution constrains phi solution)

14 P460 - 3D S.E.14 Spherical Harmonics The product of the theta and phi terms are called Spherical Harmonics. Also occur in E&M. See Table on page 127 in book They hold whenever V is function of only r. Saw related to angular momentum

15 P460 - 3D S.E.15 3D Schr. Eqn.-Radial Eqn. For V function of radius only. Look at radial equation. L comes in from theta equation (separation constant) can be rewritten as (usually much, much better...) and then have probability

16 P460 - 3D S.E.16 3D Schr. Eqn.-Radial Eqn. note L(L+1) term. Angular momentum. Acts like repulsive potential and goes to infinity at r=0 (ala classical mechanics) energy eigenvalues typically depend on 2 quantum numbers (n and L). Only 1/r potentials depend only on n (and true for hydrogen atom only in first order. After adding perturbations due to spin and relativity, depends on n and j=L+s.

17 P460 - 3D S.E.17 Particle in spherical box Good first model for nuclei plug into radial equation. Can guess solutions look first at l=0

18 P460 - 3D S.E.18 Particle in spherical box l=0 boundary conditions. R=u/r and must be finite at r=0. Gives B=0. For continuity, must have R=u=0 at r=a. gives sin(ka)=0 and note “plane” wave solution. Supplement 8-B discusses scattering, phase shifts. General terms are

19 P460 - 3D S.E.19 Particle in spherical box ForLl>0 solutions are Bessel functions. Often arises in scattering off spherically symmetric potentials (like nuclei…..). Can guess shape (also can guess finite well) energy will depend on both quantum numbers and so 1s 1p 1d 2s 2p 2d 3s 3d …………….and ordering (except higher E for higher n,l) depending on details gives what nuclei (what Z or N) have filled (sub)shells being different than what atoms have filled electronic shells. In atoms: in nuclei (with j subshells)

20 P460 - 3D S.E.20 H Atom Radial Function For V =a/r get (use reduced mass) Laguerre equation. Solutions are Laguerre polynomials. Solve using series solution (after pulling out an exponential factor), get recursion relation, get eigenvalues by having the series end……n is any integer > 0 and L<n. Energy doesn’t depend on L quantum number. Where fine structure constant alpha = 1/137 used. Same as Bohr model energy

21 P460 - 3D S.E.21 H Atom Radial Function Energy doesn’t depend on L quantum number but range of L restricted by n quantum number. l<n  n=1 only l=0 1S n=2 l=0,1 2S 2P n=3 l=0,1,2 3S 3P 3D eigenfunctions depend on both n,L quantum numbers. First few:

22 P460 - 3D S.E.22 H Atom Wave Functions

23 P460 - 3D S.E.23 H Atom Degeneracy As energy only depends on n, more than one state with same energy for n>1 (only first order) ignore spin for now Energy n l m D -13.6 eV 1 0(S) 0 1 -3.4 eV 2 0 0 1 1(P) -1,0,1 3 -1.5 eV 3 0 0 1 1 -1,0,1 3 2(D) -2,-1,0,1,2 5 1 Ground State 4 First excited states 9 second excited states

24 P460 - 3D S.E.24 Probability Density P is radial probability density small r naturally suppressed by phase space (no volume) can get average, most probable radius, and width (in r) from P(r). (Supplement 8-A)

25 P460 - 3D S.E.25 Most probable radius For 1S state Bohr radius (scaled for different levels) is a good approximation of the average or most probable value---depends on n and L but electron probability “spread out” with width about the same size

26 P460 - 3D S.E.26 Radial Probability Density

27 P460 - 3D S.E.27 Radial Probability Density note # nodes

28 P460 - 3D S.E.28 Angular Probabilities no phi dependence. If (arbitrarily) have phi be angle around z-axis, this means no x,y dependence to wave function. We’ll see in angular momentum quantization L=0 states are spherically symmetric. For L>0, individual states are “squished” but in arbitrary direction (unless broken by an external field) Add up probabilities for all m subshells for a given L get a spherically symmetric probability distribution

29 P460 - 3D S.E.29 Orthogonality each individual eigenfunction is also orthogonal. Many relationships between spherical harmonics. Important in, e.g., matrix element calculations. Or use raising and lowering operators example

30 P460 - 3D S.E.30 Wave functions build up wavefunctions from eigenfunctions. example what are the expectation values for the energy and the total and z- components of the angular momentum? have wavefunction in eigenfunction components

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