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## Main Question or Discussion Point

any CASTEP users or DFT planewave-pseudopotential method users out there?

how do I ensure that the basis set is adequate? I'm performing calculations with a rather

large unit cell ( orthorhombic, 8 atoms/cell) of a compound AB.

Can I justify my choice of energy-cutoff by testing convergence on a smaller cell of AB eg the B2 structure? then using the energy-cutoff that is found adequate for the small cell to do calculations for the orthorhombic cell?

how do I ensure that the basis set is adequate? I'm performing calculations with a rather

large unit cell ( orthorhombic, 8 atoms/cell) of a compound AB.

Can I justify my choice of energy-cutoff by testing convergence on a smaller cell of AB eg the B2 structure? then using the energy-cutoff that is found adequate for the small cell to do calculations for the orthorhombic cell?