Re: Kb, Ktheta values for TIP3P water model

From: Hadi (dinpajooh_at_gmail.com)
Date: Tue Jul 29 2014 - 17:59:19 CDT

Hi,

Below you can find the parameters of the modified TIP3P model (CGenFF:
Parameters for the Charmm General Force Field). This model is often used in
NAMD.

BONDS
!V(bond) = Kb(b - b0)**2
!
!Kb: kcal/mole/A**2
!b0: A
!
!atom type K
HT HT 0.00000 1.5139 ! ALLOW WAT
OT HT 450.000 0.9572 ! ALLOW WAT

ANGLES
!
!V(angle) = Ktheta(Theta - Theta0)**2
!
!V(Urey-Bradley) = Kub(S - S0)**2
!
!Ktheta: kcal/mole/rad**2
!Theta0: degrees
HT OT HT 55.000 104.5200 ! ALLOW WAT
HT HT OT 00.000 37.74000 ! ALLOW WAT

!
!V(Lennard-Jones) = Eps,i,j[(Rmin,i,j/ri,j)**12 - 2(Rmin,i,j/ri,j)**6]
!
!epsilon: kcal/mole, Eps,i,j = sqrt(eps,i * eps,j)
!Rmin/2: A, Rmin,i,j = Rmin/2,i + Rmin/2,j
!
!atom ignored epsilon Rmin/2 ignored eps,1-4 Rmin/2,1-4

HT 0.0000 -0.046000 0.224500 ! ALLOW WAT
                !TIP3P HYDROGEN PARAMETERS, adm jr., NBFIX obsolete
OT 0.0000 -0.152100 1.768200 ! ALLOW WAT

Regards,
Hadi Dinpajooh

On Tue, Jul 29, 2014 at 2:38 PM, Viswanath Pasumarthi <
v.pasumarthi_at_iitg.ernet.in> wrote:

> Hi,
>
> I have been trying to study interface between bulk phases of chloroform
> and water. I am following the TIP3P model for water proposed in Jorgensen
> et al. 2003 (http://dx.doi.org/10.1063/1.445869). In the force field
> parameters, what should be the Kb, Ktheta values be provided since TIP3P
> considers water to be a rigid monomer. If I take their values as 0, the
> system is undergoing chaos with each individual atom undergoing
> unreasonable displacements. If I take their values as high as 1000, the
> system is not minimizing.
>
> Thank you,
> Viswanath.
>
>

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