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Alex Granovsky
gran@classic.chem.msu.su

The default solver is SOLVER=CONJG, a preconditioned conjugate
gradient solver. The convergence criteria can be changed using
$cphf cptol variable. The default is cptol=1.0d-5. While this
criterion is interpreted a bit differently for SOLVER=CONJG and
for SOLVER=DIIS, its default value guarantees that residual errors
in the approximate solution of the CPHF equations do not result
in errors in the computed wavenumbers larger than, say, 0.01 cm^-1 or so.

The DIIS solver is usually more accurate than GONJG solver.
It also uses less memory. However, it is slower than conjugate
gradient solver.

Some additional documentation on the keywords of the $cphf input
group can be found here

Hope this helps.

Kind regards,
Alex Granovsky




On Wed Sep 19 '12 3:08am, Patrick SK Pang wrote
-----------------------------------------------
>Dear Alex,

>What is the default solver for the analytic Hessian calculation?
>How could I change the convergence criteria? Does the change in the convergence criteria affect the results significantly? I have many results calculated by the default solver. However, my computer has not sufficient memory so I use the DIIS solver to calculate several large molecules.

>Thanks!

>Regards,

>Patrick

>On Mon Sep 17 '12 9:31pm, Alex Granovsky wrote
>----------------------------------------------
>>Hi,

>>>1. I have added $CPHF SOLVER=DIIS $END in the input file. The analytic Hessian calculation is still proceeding when MAXIMUM RESPONSE ERROR is down to E-6. However, without SOLVER=DIIS, the calculation can normally terminate and complete at MAXIMUM RESPONSE ERROR down to E-6. Why?

>>Because different solvers use different convergence criteria.

>>>2. How can I restart the analytic Hessian calculation?

>>Sorry, it's impossible.

>>Regards,
>>Alex Granovsky