Selects what should be mixed during the SCF cycle. Note that currently the exact-exchange part of hybrid functionals is not mixed at all, which would require wavefunction-mixing, not yet implemented. This may lead to instabilities in the SCF cycle, so starting from a converged LDA/GGA calculation is recommended for hybrid functionals. The default depends on the TheoryLevel and the exchange-correlation potential used.
No mixing is done. This is the default for independent
The Kohn-Sham potential is mixed. This is the default for other cases.
Mix the density.
(Experimental) Mix the states. In this case, the mixing is always linear.
The linear, Broyden and DIIS scheme depend on a "mixing parameter", set by this variable. Must be 0 < Mixing <= 1.
(Experimental) If set to yes, Octopus will use a preconditioner for the mixing operator. This preconditioner is disabled for systems with dimension other than 3.
In the DIIS mixing it is benefitial to include a bit of residual into the mixing. This parameter controls this amount.
In the Broyden and Bowler_Gillan schemes, the mixing is restarted after the number of iterations given by this variable. Set this to zero to disable restarting the mixing.
The scheme used to produce, at each iteration in the self-consistent cycle that attempts to solve the Kohn-Sham equations, the input density from the value of the input and output densities of previous iterations.
Simple linear mixing.
Broyden scheme [C. G Broyden, Math. Comp. 19, 577 (1965);
D. D. Johnson, Phys. Rev. B 38, 12807 (1988)].
The scheme is slightly adapted, see the comments in the code.
For complex functions (e.g. Sternheimer with EMEta > 0), we use the generalization
with a complex dot product.
Direct inversion in the iterative subspace (diis)
scheme [P. Pulay, Chem. Phys. Lett., 73, 393
(1980)] as described in [G. Kresse, and J. Hurthmueller,
Phys. Rev. B 54, 11169 (1996)].
The Guaranteed-reduction modification of the Pulay scheme by
Bowler and Gillan [D. R. Bowler and M. J. Gillan,
Chem. Phys. Lett. 325, 473 (2000)].
When this variable is set to a value different than 1 (the default) a combined mixing scheme will be used, with MixInterval
- 1 steps of linear mixing followed by 1 step of the selected
mixing. For the moment this variable only works with DIIS mixing.
In the Broyden and Bowler_Gillan schemes, the new input density or potential is constructed from the values of the densities/potentials of a given number of previous iterations. This number is set by this variable. Must be greater than 1.