# DIIS SCF in UHF and UDFT

*From*: Ed Brothers <enb108 ^at^ psu.edu>
*Organization*: PSU Merz Group
*Subject*: DIIS SCF in UHF and UDFT
*Date*: Wed, 15 May 2002 11:20:59 -0400

I am currently implementing DIIS to accelerate SCF convergence as
per Pulay, J. Comp. Chem., V 3, #4, 556-60, 1982. In the RHF
case the construction of the error vectors is fairly straight forward:
e(i) = F(i) D(i) S - S D(i) F(i)
Where i is the step index, F is the operator matrix, D is the total
density matrix, and S is the overlap matrix. I am a bit unsure how to
proceed
with the unrestricted case. I have implemented
e(i) = Fa(i) Da(i) S - S Da(i) Fa(i) + Fb(i) Db(i) S - S Db(i)
Fb(i)
Where the a and b are the alpha and beta electron versions of the
matrix. This causes the generation of of a single B matrix and thus a
single set of coefficients from the linear equation.
Is this the right way to set up the error matrix for step i in UHF and
UDFT? If it isn't, what is? Dose anyone know a reference where this
is discussed?
Thanks for your time.
Ed Bothers.
Merz Goup, Penn State
enb108 ^at^ psu.edu