ChE 230A Final Exam December 10, 2009 f have not seen as far as others, it is because giants were standing on my shoulders. - H. Abelson 1) Show that eigenvalues (λ) in the Sturm-Liouville problem below are positive if q(x) > 0. Hint: consider the inner product of the equation with y(x). y'' + q( x) y = λ y a< x< b ya ( ) = yb ( ) = 0 2) a) For functionals F[y(x)], G[y(x)], and Λ[y(x)] = F[y(x)]/G[y(x)], show that δλ= [δf - ΛδG]/G How did we use this result in class? Hint: F[y(x)]-λG[y(x)]. δ f( x0 ) b) Show that = δ[ x x0 ] δ f( x) c) Maragliano et al. [J. Chem. Phys. 2006] showed that the optimal reaction coordinate in a space of coarse grained variables minimizes the functional F [ q( z)] = dze β zq M( z ) zq (M(z) is symmetric). Express δ/δq(z) as a divergence of a field in z-space. 3) Short answer: a) For a Hermitian operator L, what must be true of the spectrum for a Green's function to exist? b) To reformulate a Sturm-Liouville problem as a matrix problem you choose basis functions {u k (x)} that satisfy the homogeneous boundary conditions. The matrix A is defined by A ij = <u i (x) L u j (x)>. Will A be Hermitian? Explain. 4) n the local density approximation (Thomas and Fermi), the potential φ(r)
around an atom satisfies 2 = φ() r 4 πρ() r 4 π Zδ[] r where ρ(r) is a charge cloud from the electrons and the delta function is from the charged nucleus at the origin. Both ρ(r) and φ(r) approach zero as r. n the homework you showed 2 (1/ r) = 4 πδ[ r ]. Use this result from your homework to give an expression for φ. Do not try to simplify your result. f you don't see how to use the result above, you might be able to give an answer by another approach. 5) Linear Response Theory: Suppose that at time t=0 a unit electric field is applied to a dielectric body. An electric dipole moment of size μ(t) in the direction of the field would be induced in the body. nstead, an oscillating field is applied, E(t) = Ecos(ωt). Give an expression for μ(t) assuming the unit step response is increases continuously from zero. For three bonus points, give the derivation of the principle you are using. 6) Use the relation from Laplace Transforms: to show that 0 st y'( t) e dt = syˆ ( s) y(0) y( ) = lim s yˆ ( s) s 0
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