I am new to DFT-simulation and I wish to understand how it works behind the scene. As the title suggests I don't understand why LCAO-based codes have to define K-points and cut-off energies. I understand why they are used in Plane-Wave codes. In such codes the cut-off energy defines the max G value of the Fourier series and the k-point defines how fine the Monkhorst-Pack grid is defined. However, in LCAO we work in real space, so both parameters are not inherent to the representation used.
How I understand it now, the K-point is defined to determine how fine the real-space grid is discretized, but I exactly understand how and why this is used instead of using a real-space discretization variable. If this is the case, I still don't see what purpose the Energy cut-off has.
Could someone help me with this or point me in the direction of some resources on this?