[gmx-users] Steepest descent vs Conjugate gradient energies

[David van der Spoel]

On Mon, 21 Jan 2002, Andrew Horsfield wrote:

>Hi,
>
>I get different energies from using steepest descent and conjugate
>gradient optimizers. (I a using gromacs 3.0.5, with PME for
>electrostatics). The problem appears to be that the long ranged coulomb
>term is not included in the steepest descent calculation:
>
>Steepest descent
>----------------
>   Energies (kJ/mol)
>           Bond          Angle    Proper Dih.  Improper Dih.          LJ-14
>    2.59408e+02    9.03184e+02    6.64435e+02    2.15660e+02    1.03799e+03
>     Coulomb-14        LJ (SR)   Coulomb (SR)   Coulomb (LR)      Potential
>    1.64964e+04   -7.15170e+03   -5.94253e+03    0.00000e+00    6.48285e+03
>    Kinetic En.   Total Energy    Temperature Pressure (bar)
>    0.00000e+00    0.00000e+00    0.00000e+00    0.00000e+00
>
>Conjugate gradient
>------------------
>   Energies (kJ/mol)
>           Bond          Angle    Proper Dih.  Improper Dih.          LJ-14
>    2.59488e+02    9.02182e+02    6.64151e+02    2.15576e+02    1.03894e+03
>     Coulomb-14        LJ (SR)   Coulomb (SR)   Coulomb (LR)      Potential
>    1.64972e+04   -7.15239e+03   -5.94202e+03   -2.35473e+04   -1.70643e+04
>    Kinetic En.   Total Energy    Temperature Pressure (bar)
>    0.00000e+00    0.00000e+00    0.00000e+00    0.00000e+00
>
>Is there a reason for this?
No this is a bug. It has been fixed in the development version. By the way
I think it is th eother way around...

Groeten, David.
________________________________________________________________________
Dr. David van der Spoel, 	Biomedical center, Dept. of Biochemistry
Husargatan 3, Box 576,  	75123 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://zorn.bmc.uu.se/~spoel
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