Real-Space Grid

Siesta solves the DFT equations on a real-space grid. The density of this grid is one of the most important parameters for controlling the accuracy and cost of a calculation.

• Mesh.Cutoff: This parameter controls the grid's fineness. It's an energy cutoff, analogous to the plane-wave cutoff in other DFT codes. Higher values lead to a denser grid, increasing accuracy but also computational cost. Typical values range from 200 Ry for simple systems to 500 Ry or more for high-accuracy calculations.
• Eggbox Correction: The discrete nature of the grid can cause a small, artificial energy corrugation known as the "eggbox effect." Enabling this option applies a correction to mitigate this error, which can be important for very accurate energy difference calculations or smooth potential energy surfaces.