[gmx-users] Carbon Nanotube Force Field

[Jian Zou]

Sorry for my typos.

> Date: Tue, 02 Aug 2005 19:42:37 +0200
> From: David <spoel at xray.bmc.uu.se>
> Subject: Re: [gmx-users] Carbon Nanotube Force Field
> To: Discussion list for GROMACS users <gmx-users at gromacs.org>
> Message-ID: <1123004557.6026.8.camel at localhost.localdomain>
> Content-Type: text/plain

> On Tue, 2005-08-02 at 12:18 -0400, Bob Johnson wrote:
>> Hello,
>> I'm simulating a system involving carbon nanotubes. As an initial test of
>> my
>> force field I want to simulate a single infinite carbon nanotube. I've
>> done
>> simulations at constant volume and constant pressure. I've also run some
>> energy
>> minimizations. However, it seems that the energy is always too high and
>> the tube
>> wants to develop kinks and collapse on itself. I'm using the following
>> force
>> field obtained from the following paper: Guo, Karasawa, Goddard, Nature,
>> Vol.
>> 351, 1991

>>
>> Bonds:
>> Morse potential (function 3 in GROMACS)
>> D = 478.9 kJ/mol
>> b_0 = 0.1418 nm
>> beta = 21.867 nm^-1

>> Angles:
>> G96 angle (function 2 in GROMACS)
>> theta_0 = 120.00
>> fc = 562.2 kJ/mol

> Check fc, units are not correct.
The units should be right.

>>
>> Dihedrals:
>> Proper dihedral (function 1 in GROMACS)
>> theta_max = 180.00
>> fc = 12.06 kJ/mol
>> mult = 2

>> Pairs:
>> L-J (function 1 in GROMACS)
>> c6 = 4*eps*sig^6 = 5.7353e-3 kJ nm^6/mol
>> c12 = 4*eps*sig^12 = 1.8707e-5 kJ nm^12/mol

C6, C12 values may be wrong.

Did you take these data from Koumoutsakos et al.'s JPCB paper (or Carbon
paper), or Tuzun et al.'s Nanotechnology paper, and not directly from Guo et
al.'s Nature paper?

In Koumoutsakos et al.'s Paper, they used sigma_CC and epsilon_CC for LJ
parameters.
But in my opinoin the parameters are acturally for R_CC and epsilon_CC,
where R_CC = sigma_CC * 2^(1/6).
You may check the original Nature paper and reference therein, and also
Rappe's JACS paper about UFF to confirm this.


>> Can anyone verify that this is correct? Any suggestions on stabilizing
>> the
>> nanotube?
>> Thanks,
>> Bob


Regards,

Jian Zou