[gmx-users] Re: cutoff problem

[Vitaly V. Chaban]

On Thu, Mar 25, 2010 at 12:45 AM, XAvier Periole <x.periole at rug.nl> wrote:
>
> On Mar 24, 2010, at 10:58 PM, Vitaly V. Chaban wrote:
>
>>> Hi,
>>>
>>> I want to test different values of cutoff for vdw. However, in the list
>>> someone said cutoff = 0.9 for vdw was used for paramaterizing of >Gromos
>>> force field, other values would cause error, and also there was someone
>>> saying that cutoff for vdw should be set to 1.4. Can >someone make this
>>> question clear? Thanks a lot.
>>
>> The common rule for all FFs is to set the LJ-cutoff around
>> 2.5*sigma(LJ12-6). In fact, you'll get about 0.9 nm for the most
>> objects. I see nothing terrible if you use, say, 1.4 nm just because
>> the difference will be negligible.
>
> Where is that coming from? This is so wrong!

>From the properties of LJ12-6 curve.

>> Just test it. :)
>
> I've you ever tried that on a lipid bilayer?

My interests are a bit shifted from bilayers. What concrete atom pair
will cause the problem in your example?

> Who could ever say (whatever force field) a vdW cutoff of 0.9/1.4 nm
> is no difference?
>>
>> --
>> Dr. Vitaly Chaban
>> --