Question: Multibarrier Problem - Schroedinger

Dear all,

I am trying to simulate the penetration of the wavefunction into a potential barrier consisting of two barrier steps of different heights, V1 and V2.

My code looks like that:

> restart;
> m := 0.91e-30;h := 0.1055e-33; V1 := 10*0.16e-18; V2 := .8*V1;a := 0.10e-9;En := .6*V1; w := En/h;
                                      
> k1 := sqrt(2*m*En)/h; kappa2 := sqrt(2*m*(V1-En))/h; kappa3 := sqrt(2*m*(V2-En))/h;
                       
> psi1 := x-> exp(I*k1*x)+B*exp(-I*k1*x);
> psi2 := x-> F*exp(kappa2*x)+G*exp(-kappa2*x);
> psi3 := x-> H*exp(kappa3*x)+K*exp(-kappa3*x);
> psi4 := x-> C*exp(I*k1*x);
> Sol := solve({psi1(0) = psi2(0), psi2(a) = psi3(a), psi3(2*a) = psi4(2*a), (D(psi1))(0) = (D(psi2))(0), (D(psi2))(a) = (D(psi3))(a), (D(psi3))(2*a) = (D(psi4))(2*a)}, {B, C, F, G, H, K});
            {B = 0.2047826094 - 0.9270172771 I, C = -0.1788702634 - 0.2582798479 I, F = 0.03471147699 + 0.02346057170 I, G = 1.170071132 - 0.9504778488 I, H = 0.01427455243 + 0.07254519326 I, K = 1.005502004 - 0.8781369751 I}
> assign(Sol);
> br := piecewise(x < 0, 0, `and`(0 < x, x < a), V1/En, `and`(a < x, x < 2*a), V2/En, x > a, 0);
> with(plots);
> Epr11 := evalc(conjugate(psi1*psi1));
> Epr12 := simplify(Epr11);
> Epr13 := evalc(conjugate(psi2*psi2));
> Epr14 := simplify(Epr13);
> Epr15 := evalc(conjugate(psi3*psi3));
> pr16 := simplify(Epr15);
> ppot := plot(br, x = -4*a .. 4*a);
> pb1 := plot(Epr12, x = -4*a .. 0);

Warning, unable to evaluate the function to numeric values in the region; see the plotting command's help page to ensure the calling sequence is correct

Whats wrong with that code so far?

Does anybody has experience with the simulation of a triangular step?

Thanks for any help!