The momentum density has been averaged over a wavelength.

It is defined through the momentum density and the mass concentrations:

Instead of integrating over energy, we can also plot the momentum density at a certain energy.

Here the momentum density at the Fermi level.

Thanks to the mass conservation equation and to the definition of the momentum density, the first member becomes simply:

Electromagnetic waves also carry momentum - the magnitude of the momentum density.

In such cases the relevant macroscale variables are averages such as mass and momentum density.

This is what is expected, so the division by 2 in the spin contribution to the momentum density is necessary.

Notice that, in the above two formulas, the energy density and momentum density may be arbitrarily small!

It is more difficult to define momentum density in media because the division into electromagnetic and mechanical is arbitrary.

The bond directional principle has been discussed through the topological properties of electron momentum densities.

Similarly, energy density must be combined with momentum density and pressure into the stress-energy tensor.

Furthermore, the momentum density of annihilating electron-positron pairs is enhanced near the Fermi surface.

"Recent development of momentum density measurement of polyatomics by molecular (e,2e) spectroscopy."

Our quantitative analysis is based on various properties of the isotropic momentum density and on the kinetic energy anisotropy.

For a sinusoidal plane wave propagating along axis the orbital angular momentum density vanishes.

Most basis sets used in quantum chemistry are designed to get the correct charge and momentum density in the region important for covalent bonding.

The angular momentum density vector is given by a vector product as in classical mechanics:

Keywords: atomic radii, shell structure, aufbau principle, charge density, momentum density.

Expressions for the fundamental invariants and the energy density and momentum density also take on simple forms:

It is apparent that in SR the stress-energy tensor embodies a compact description of energy and momentum density.

In particular, these calculations allowed us to quantitatively discriminate kinetic energy effect induced by pressure and Jahn-Teller effect, on momentum densities.

Key words: electron momentum density, the bond directional principle, topological analysis, first-row hydrides, homonuclear diatomic molecules.

Topological analysis of electron momentum densities of the first-row hydrides and homonuclear diatomic molecules has been carried out.