# [gmx-users] Box dimension

Alex nedomacho at gmail.com
Mon Jun 4 09:33:56 CEST 2018

```I'm kind and civil, practically a sweetheart. I just can't put smiley
faces everywhere! On the other hand, it does not hurt to try things and
have a little bit of initiative. I don't know why I am telling you this,
like you've never supervised students... Also, CNTs are simulated
exactly the same way (within these forcefield flavors) as pretty much
anything else you can think of. That is, until one day when you guys
decide to come with a testing Gromacs version that includes FFs not
relying on permanent topologies. ;)

Alex

On 6/4/2018 1:28 AM, Mark Abraham wrote:
> Hi,
>
> Let's keep the discussion kind and civil, please. What's obvious when you
> have experience often isn't when you are new. :-) I sure don't understand
> the arithmetic involved, but then I've never attempted a CNT simulation!
>
> Mark
>
> On Mon, Jun 4, 2018, 09:08 Alex <nedomacho at gmail.com> wrote:
>
>> And again, your question has nothing to do with Gromacs. It has to do
>> with what you want to do, common sense, and basic arithmetic.
>>
>> CNTs interact at pretty short range (if they are intact and without edge
>> passivation), so I'd just go with a distance sweep range of ~1.5 nm and
>> give it some additional space, say, 1 nm, and finally keep the box
>> symmetric. With CNT diameter of 1.3 nm, this would be (1.3 + 1.5 + 1) x
>> 2 = 7.6 nm. You could of course place the CNT off center (in Z) to
>> shorten the box.
>>
>> Alex
>>
>>
>> On 6/4/2018 12:53 AM, rose rahmani wrote:
>>> Hi,
>>>
>>> I want to do umbrella sampling for different coordination of amino acid
>>> through different distances (in Z dimension) from nanotube. The nanotube
>>> axis is along X axis. The COM of nanotube is in Z=1.5 and its outer
>>> curvature(which is in touch with amino acid) is in Z=1.5 +0.65=2.15
>>> (because the nanotube radius is 0.65nm). The initial distance of amino
>> acid
>>> from nanotube is 2nm. The question is how should i choose the box Z
>>> dimension that some artifacts (justin explained in tutorial) doesn't
>>> happen? I choose 7nm, is it ok or large?
>>>
>>>
>>> Best regards
>>> -Rose
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```