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

[binju... at gmail.com]

Dear Dawid, Thanks for you answer, I am using the standard Amber 
forcefield. 

best

binju 

在 2018年6月6日星期三 UTC+8下午5:15:03，Dawid das写道：

> 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.
>
> 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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