I have some trouble understanding what to do when the effective mass in a heterostructure depends on position. Suppose for example that you have two materials, which are put together such that in one region the kinetic energy is described by one effective mass and in the other region another. How do you incorporate this into the Hamiltonian? My first guess was to simply say that the kinetic energy is: -ħ2/2m*(x) ∂2/∂x2 But thinking about it further I guess this does not work, since H is now no longer Hermitian necessarily. I looked up solutions for this and apparently the kinetic energy operator that does the job is: -ħ2∂/∂x[1/m*(x)∂/∂x] Now I am not sure how to see that this is indeed hermitian? Can anyone help me realize that?