CCL:G: software to optimize a large molecule



 Sent to CCL by: Paul Fleurat-Lessard [Paul.Fleurat-Lessard__ens-lyon.fr]
 Hi,
 
It seems that you want to use DFT. I think that one option not yet mentionned would be to use a QM:QM' or QM:MM approach. With this hybrid scheme you can use DFT for the metal and its close surrounding and then either a semi-empirical or MM level for the rest of the molecule.
 
Concerning the geometry optimization efficiency, in my experience, Gaussian is really good for this task, but it is not free.
 
In any case, it might be a good option to pre-optimize using a 'low-cost' level such as semi-empirical or MM, and the you can optimize the molecule at the DFT level if you need.
 Regards,
 paul.
 Le 20/07/2011 07:02, psavita(~)crlindia.com a écrit :
 
 Sent to CCL by: psavita() crlindia.com
 Hello Neranjan,
 It seems you need to optimize this large molecule having no periodic boundaries.
 So it
 is going to be compute intensive for any software, whether that employs plane
 waves
 (as in abinit and QE) or Gaussians (GAMESS). For large systems, it may be better
 to use
 semiempirical (such as MOPAC) or MM (such as GULP) prior to full ab initio
 optimization.
 On the other hand, if your system is describable with a unit cell with few
 atoms, abinit or QE will be very fast.
 Your question may be fully answered if the system is properly understood.
 Best wishes,
 Savita Pundlik
 Computational Materials Applied Research Group
 Computational Research Laboratories Ltd.,
 Taco House, Damle Path, Off Law College Road
 Pune - 411004, India.
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 Fleurat-Lessard Paul,  Associate Professor
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