Energy increase with fixed atoms in POPC membrane

From: Mihaela Drenscko (quo.physics_at_gmail.com)
Date: Wed Feb 17 2016 - 16:27:15 CST

Hi,

I was following the tutorial:

http://www.ks.uiuc.edu/Training/Tutorials/science/membrane/mem-tutorial.pdf

to build a POPC membrane 50x50 with PCL (instead of kcsa), using CHARMM36.

In section 3.1, page 38, it shows how fix atoms:

set fixed [atomselect top "water or name CLA POT or protein or
\
(chain L and name O2 P1 O3 O4 O1 C15 H52 H51 H11 C11 H12
\
N C14 H42 H43 H41 C12 H22 H23 H21 C13 H33 H31 H32)"]

For the membrane pdb in charmm36, there are other notaions for atoms. I
made this change:

set fixed [atomselect top "water or name CLA POT or protein or \
(chain L and name O11 P O13 O14 O12 C11 H11B H11A H12A C12 H12B \
N C15 H15B H15C H15A C13 H13B H13C H13A C14 H14C H14A H14B)"]

Was this replacement wrong? When I run the jib, the energy does not
minimize (I increased minimization steps to 5000, decreased timestep 1 fs,
and run it for 2500 steps):

ENERGY: 7500 4446.6430 6773.7383 3764.0810
41.4892 -20222.3357 9999999999.9999 0.0000
0.0000 4719.5622 9999999999.9999 297.2827 9999999999.9999
9999999999.9999 295.0647 9999999999.9999 9999999999.9999
160380.0000 9999999999.9999 9999999999.9999

WRITING EXTENDED SYSTEM TO OUTPUT FILE AT STEP 7500
CLOSING EXTENDED SYSTEM TRAJECTORY FILE
WRITING COORDINATES TO OUTPUT FILE AT STEP 7500
CLOSING COORDINATE DCD FILE
The last position output (seq=-2) takes 0.001 seconds, 111.801 MB of memory
in use
WRITING VELOCITIES TO OUTPUT FILE AT STEP 7500

Thank you,
Mihaela

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