The exact functional of DFT can be defined by the Levy constrained search. However, there are many other constrained searches that can be carried out. In this talk, we will demonstrate a general stochastic procedure that can be used in a range of scenarios: (1) Create an initial state that satisfies the constraint. (2) Define a small move or sets of moves that maintains the constraint. (3) Attempt the move and work out the change in energy. (4) Repeat this many times until convergence. We apply this to optimise orbitals in Kohn-Sham and Hartree-Fock, as well as wavefunctions and ensembles in DFT. We also use linear-programming to attack the problem of carrying out a constrained search to the density-matrix with quantum-chemical basis sets.

Constrained searches in density functional and wavefunction theories

255th National Meeting (2018)

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