Formula Group Velocity (Oscillation of a Monatomic Chain) Spring constant    Mass    Lattice constant    Wave number

Group velocity

Unit
Velocity with which a lattice vibration propagates in the crystal. It follows from the derivative of the dispersion relation $$\omega(k)$$ of the lattice vibration with respect to the wavenumber $$k$$.

Spring constant

Unit
Spring constant for the coupling between neighboring lattice planes (atomic chains) of the crystal lattice.

Mass

Unit
Mass of an atom inside a lattice chain.

Lattice constant

Unit
Lattice constant is the distance between adjacent lattice planes at equilibrium.

Wave number

Unit
Wavenumber represents the number of oscillations performed within the wavelength $$\lambda$$: $$k = \frac{2\pi}{\lambda}$$. The sign of the wavenumber indicates the direction of propagation of the oscillation.