San José State University |
---|
applet-magic.com Thayer Watkins Silicon Valley, Tornado Alley & the Gateway to the Rockies USA |
---|
Schrodinger Equation and the Time-Spent Probability Density Function |
---|
Let H(p, x) be the Hamiltonian function for a physical system. If H does not explictly
involve time then it is the same as total energy E, kinetic and potential. Then let H^(∇, x) be its
Hamiltonian operator, where momentum p is replaced by ih∇, h
is Planck's constant divided by 2π and i is the square root of negative one.
The time-independent Schrödinger equation for the system is the
For a particle of mass m in a potential field V(x), H^((∇x, x) is of the form
Thus the time-independent Schrödinger equation is
where μ(x)=(2m)/h²
The probability density for a particle at point s of its trajectory when moving at a velocity v is given by
where T is the total time taken to execute the periodi trajectory.
By Hamiltonian analysis the velocity v(x) is given by
For the Hamiltonian function of a particle is a potential field H=p²/2m + V(x)
But for this case
This can be rewritten as
½
In general, velocity may be expressed as a function of kinetic energy K(x)=E−V(x)=E(1−V(x)/E).
Therefore the wavefunction σ(x) associated with the time-spent probability density function PTS(x) is given by
Now let λ(x) be defined by
Now the Schrödinger equation
must be evaluated and that starts with the Laplacian ∇².
The Laplacian is the divergence of the gradient of a scalar field; i.e.,
The Laplacian ∇² of the product of two functions f·g is given by
Again for typographic convenience let J(x)−¼= μE(H(x))−¼
and thus J(x)=(μE)4H(x). Therefore
Therefore
Note that
Since
Therefore
Multiplying through by J¼(z) gives
Note that
and ∇V(z) and ∇²V(z) are fixed as E→∞.
Therefore all of the terms on the LHS of the previous equation above except (∇²λ)
go to zero as E increases without bound. They approach zero
because they have a derivative of J in their numerators involving E³ and a power of J in their denominators involving
a power of E4.
Furthermore H(z) asymptotically approaches
1 as E→∞. Thus λ(z) asymptotically approaches the solution to
the equation
This is a Helmholtz equation.
Its solutions in Cartesian coordinate systems are sinusoidal.
The values of λ² then oscillate between a maximum
value and zero. This function λ(x) could called the flutter function for the system.
Its spatial average is a constant. See Helmholtz equation averages.
The fact that the coefficient of the Helmholtz equation is proportional to the fourth power of energy
means that as E increases the solution very quickly goes to ultradense fluctuations of probability density such
that any degree of spatial averaging results is a close approximation of the Classical time-spent probability
density distribution.
So the probability density λ(z)² generally consists of a function which oscillates
between relative maxima and zero values. The spatial average of that
function is a constant. Therefore the probability densities are inversely
proportional to J(x)½=(1-V(x)/E)½
just as the classical time-spent
probabilities are.
φ(z) = λ(z)(J(x))−¼
∇²φ =(∇²λ)(J−¼)
+ 2(∇λ)·∇(J−¼) + λ(∇²(J−¼))
∇(J−¼) = −(1/4)(J−5/4)∇J(z)
and
∇²(J−¼) = −(1/4)(J−5/4)∇²J(z)
+ (5/16)(J−9/4)(∇J(z))² − (1/4)(J−5/4)∇²(J(z))
∇²φ = − J(z)φ(z) = − J(z)λ(z)J−¼
and hence
∇²φ = − λ(z)J¾(z)
(∇²λ)(J−¼) − 2(1/4)J−5/4)(∇λ)·(∇J)
+ λ(z)[−(1/4)(J−5/4)∇²J(z)
+ (5/16)(J−9/4)(∇J(z))² − (1/4)(J−5/4)∇²(J(z))]
= − λ(z)J¾(z)
(∇²λ) − (1/2)J−1)(∇λ)·(∇J)
+ λ(z)[−(1/4)(J−1)∇²J(z)
+ (5/16)(J−2)(∇J(z))² − (1/4)(J−1)∇²(J(z))]
= − λ(z)J(z)
∇J(z) = −(μE)4∇V(z)/E = −μ4E3∇V(z)
and
∇²J(z) = −∇²(μE)4V(z)/E = −μ4E3∇²V(z)
∇²λ(z) = −(μE)4λ(z)
HOME PAGE OF
Thayer Watkins,