  Revisiting the issue associated with Position-Dependent Mass (PDM), we
reaffirm that the appropriate framework for addressing a generic PDM is the
symmetrization proposed by BenDaniel and Duke. To accomplish this result adopts
the effective mass Hamiltonian proposed by von Roos, corrected by a symmetrized
kinematic term. After verifying the appropriate ordering to approach the PDM
issue, one investigates a crystalline lattice with a defect described by a
singular PDM. The singular mass profile proves intriguing as it yields an
atom's cluster in the neighborhood of the singularity. Considering that a
restoring force acts on the atoms, one notes that the confluent Heun function
describes the quantum states. Furthermore, one highlights that when the
effective mass distribution tends to a constant profile, we recover a system
similar to the harmonic oscillator.
