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Bug #1527

mass contribution to dH/dlambda has wrong sign

Added by Berk Hess over 4 years ago. Updated over 4 years ago.

Status:
Closed
Priority:
Normal
Assignee:
Berk Hess
Category:
mdrun
Target version:
4.6.6
Affected version - extra info:
Affected version:
4.6
Difficulty:
uncategorized
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Description

Commit b8440aeb incorrectly change the sign of the kinetic contribution to dH/dl. The commit message says:

in update.c, in calc_ke_part_normal and calc_ke_part_visc

  • sign error in mass change; if mass B is greater than mass A, then the
    change in free energy is positive, not negative.

This is incorrect, if massB is greater the free-energy change is negative. The kinetic contribution is obtained from the derivative of p^2/(2*mass(lambda) which has the opposite sign.

The fix is only a sign change (plus a comment explaining this tricky sign issue).
Since mass contributions vanish is a thermodynamic cycle, I don't know if we should fix this for 4.6.6 or for 5.0.

Associated revisions

Revision 07f2d6a9 (diff)
Added by Berk Hess over 4 years ago

Fixed the sign of mass perturbed contribution

Corrected the sign of the kinetic energy contribution to dHdl and dH.

Fixes #1527.

Change-Id: Ia1a2f708cdbba9a5a120a2ba8510cc2498f4d054

History

#1 Updated by Mark Abraham over 4 years ago

  • Description updated (diff)

#2 Updated by Gerrit Code Review Bot over 4 years ago

Gerrit received a related patchset '1' for Issue #1527.
Uploader: Berk Hess ()
Change-Id: Ia1a2f708cdbba9a5a120a2ba8510cc2498f4d054
Gerrit URL: https://gerrit.gromacs.org/3681

#3 Updated by Berk Hess over 4 years ago

  • Status changed from New to Fix uploaded
  • Target version set to 4.6.6

#4 Updated by Erik Lindahl over 4 years ago

  • Status changed from Fix uploaded to Resolved

#5 Updated by Erik Lindahl over 4 years ago

  • Status changed from Resolved to Closed

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