I have a 3D charge density file, calculated from Quantum Espresso DFT.
If someone calculates the total charge (number of electrons) of an unit cell from that cube file (using a numerical approximation method, for example, a spherical integration), what should be the basic mathematical equation to express that?
If needed to see the charge density file: 3D cube file
Now need to know the equation for total charge (using spherical integration) for the 3D cube file of charge density. Thanks in advance.