Why to use a scaling factor for both vdw and electrostatics in QM/MM calculations

[Dawid das]

Hello,

Whether you scale the 1-4 interctions or not depends on the force field and 
system (lipid, protein, nucleic 
acid). For instance, I use CHARMM22 force field and I do not scale the 1-4 
interactions (VDW_SCALE14 and EI_SCALE14 set to 1.0).

You need to read how your force field was optimized and what scaling factor 
(if any) is suggested.

Also I do not really see reason to do rescaling for QM/MM and not for 
classical simulations. Plausibly 
this rescaling is just related to FF type.

Best wishes,
Dawid

W dniu środa, 6 czerwca 2018 11:09:41 UTC+2 użytkownik binj... at gmail.com 
napisał:
>
> I saw most of QM/MM input use the scaling factor for both vdw ( 
> VDW_SCALE14 0.5)  and  electrostatics  ( EI_SCALE14 0.8333333).
> It is not clear to me why we need to do this, since we did not us the 
> scaling factor in the classical MD, and the forcefield works well in the 
> classical MD.
> Now, we invoke the same forcefield in QM/MM calculation, but we need to 
> scale the vdw and  electrostatics ?  Thanks!
>
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