  Large-scale density functional theory (DFT) calculations provide a powerful
tool to investigate the atomic and electronic structure of materials with
complex structures. This article reviews a large-scale DFT calculation method,
the multi-site support function (MSSF) method, in the CONQUEST code. MSSFs are
linear combinations of the basis functions which belong to a group of atoms in
a local region. The method can reduce the computational time while preserving
accuracy. The accuracy of MSSFs has been assessed for bulk Si, Al, Fe and NiO
and hydrated DNA, which demonstrate the applicability of the MSSFs for varied
materials. The applications of MSSFs on large systems with several thousand
atoms, which have complex interfaces and non-periodic structures, indicate that
the MSSF method is promising for precise investigations of materials with
complex structures.
