[gmx-users] Lambda Dependence when delta_lambda = 0

[David van der Spoel]

On Thu, 2003-09-11 at 08:39, Ilya Chorny wrote:
> I read that in the manual but that make sense if you incriment lambda. What
> happens if delta_lambda = 0.
> Am I correct to say dh/dl = dH if delta_lambda = 0.
> 
No, it's the derivative at the lambda value you specify in init_lambda
dlambda just means how much lambda should change per timestep (or per
ps)

> Ilya
> 
> 
> 
> -----Original Message-----
> From: gmx-users-admin at gromacs.org [mailto:gmx-users-admin at gromacs.org]On
> Behalf Of David
> Sent: Wednesday, September 10, 2003 11:34 PM
> To: gmx-users at gromacs.org
> Subject: Re: [gmx-users] Lambda Dependence when delta_lambda = 0
> 
> 
> On Thu, 2003-09-11 at 00:53, Ilya Chorny wrote:
> > Hi Erik,
> >
> > I ran a short test trajectory where 100 ps calculating the free energy
> > of going from Ar - LJ1 (argon with a sigma one Angstrom smaller). In the
> > mdp file I set free energy to yes and kept the rest of the free energy
> > parameters as defaults. I'm not sure I understand what the dH/dl in the
> > case when delta_lambda = 0. Should it not just be the difference in the
> > Hamiltonians between Ar and LJ1. The numbers seem a little high (~7000
> > kJ/mol) and I would expect them to be negative.
> >
> 
> dH/dl is the derivative of the energy with respect to lambda, it may
> very well be non zero for any value of lambda. I think it is described
> in the manual..
> 
> > Thanks,
> >
> > Ilya
> >
> >
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> --
> Groeten, David.
> ________________________________________________________________________
> Dr. David van der Spoel, 	Dept. of Cell and Molecular Biology
> Husargatan 3, Box 596,  	75124 Uppsala, Sweden
> phone:	46 18 471 4205		fax: 46 18 511 755
> spoel at xray.bmc.uu.se	spoel at gromacs.org   http://xray.bmc.uu.se/~spoel
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-- 
Groeten, David.
________________________________________________________________________
Dr. David van der Spoel, 	Dept. of Cell & Mol. Biology
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://xray.bmc.uu.se/~spoel
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++