[CPMD-list] convergence problem on iron porphyrin

[Axel Kohlmeyer]

On 7/30/06, Yong Zhang <zhangymall11 at gmail.com> wrote:


dear yong,


> Axel is absolutely correct, "LOC=S" does nothing when VDBpp is used and PCG
> is essential. (I just want to double check it by my own, please do not mind
> ^_^) But the wavefunction optimization runs using MT (with PCG and LOC=S)
> died finally. Does this simply mean that MT is not appropriate for this
> calculation or I need to take care of other settings?

it is extremely difficult to create a MT pseudopotential for iron that works
well in higher oxidation states and for open shell systems. your best bet
for norm-conserving psps is to go with a goedecker semi-core psp, but
that will be extremely costly in terms of cpu time (cutoff 120ry or more).

> Both Dual=5 and Dual=6 work. And dual=5 gave a lower energy after geometry
> optimization. I suppose this is good enough.

that is not a good parameter. you have to consider the 'ripples' effect,
that affects especially geometry optimizations at low cutoff. a better
parameter would be to look for good energy conservation during MD.

> Thank Axel for the link. I guess the problem is related to the
> adiabatic/nonadiabatic dynamics of DFT method. But, to be honest, I do not

????

this problem is related to the incomplete and averaged description of electron
correlation in DFT. DFT assumes a homogeneous electron gas, but at
d-metals (or even more elements with f-electrons) you have highly localized
electrons and thus DFT leads to an unphysical smearing out of the spin
polarization.
if you have only one d-element DFT still works mostly ok for the 'all-up' and
non-magnetic non-polarized cases.

> know how to prove (or define) that my system is nonadiabatic :-(
> I did test the different spin states for my system. For spin=1,3 or 5, all
> the wavefunction jobs completed without problem. But in the GEO
> optimization, only spin=3 completed with reasonable result. This is
> consistent with previous references saying that spin=3 is the stablest state
> for this complex. But this is only a static calculation, I do not know what
> will happen if I run a dynamics.
> For spin=1 or 5, I observed a total energy jump which I believe is caused by
> the rapid increase in kinetic energy. But I do not understand why this
> happened?

what version of CPMD are you using?
this can have a number of reasons. can you send me your
inputs, so i can try to reproduce that.

axel.


> Thank you!
>
>
>
> Best wishes
>
> Yong
>
>
>


-- 
=======================================================================
Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
  Center for Molecular Modeling   --   University of Pennsylvania
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