[gmx-users] Charges in alchemistry

dgfd dgdfg roinato at mail.ru
Tue Jan 30 21:30:58 CET 2018


Good day. I faced with the false dipole momentum behavour in (L)-(D) alchemistry transformation of aminoacids stereoisomers and show it on simple example.
Let's annihilate charges in CO molecule using method of two topologies and slow-growth dynamics at 0 Kelvins.

gro:
    1CO       C    1   1.500   1.500   1.440
    1CO       O    2   1.500   1.500   1.563

mdp:
integrator      =       md
dt              =       0.001
nsteps          =       100000
Tcoupl          =       V-rescale
tau_t           =       0.1
tc-grps         =       system
ref_t           =       0
init-lambda     =       0
delta-lambda    =       .00001

itp:
[ moleculetype ]
; Name            nrexcl
co             3
[ atoms ]
;   nr       type  resnr residue  atom cgnr charge   mass  typeB    chargeB      massB
     1   opls_252      1    CO      C      1    .42     12.011    opls_253         0       15.9994
     2   opls_253      1    CO      O      1    -.42    15.9994  opls_252        0       12.011
[ bonds ]
    1     2     1

After all I calculated the dipole momentum (gmx dipoles) and noticed no change in it.

Mtot.xvg :
         0  0.00000000e+00 0.00000000e+00 -2.48133469e+00 2.48133469e+00
     0.001  0.00000000e+00 0.00000000e+00 -2.48119354e+00 2.48119354e+00
     0.002  0.00000000e+00 0.00000000e+00 -2.48093224e+00 2.48093224e+00
     0.003  0.00000000e+00 0.00000000e+00 -2.48056221e+00 2.48056221e+00
.
.
.
    99.996  0.00000000e+00 0.00000000e+00 -2.47931862e+00 2.47931862e+00
    99.997  0.00000000e+00 0.00000000e+00 -2.47931862e+00 2.47931862e+00
    99.998  0.00000000e+00 0.00000000e+00 -2.47931862e+00 2.47931862e+00
    99.999  0.00000000e+00 0.00000000e+00 -2.47931862e+00 2.47931862e+00
       100  0.00000000e+00 0.00000000e+00 -2.47931862e+00 2.47931862e+00
So I am asking 3 questions.
1)  Whats' wrong?
2) How output atomic charges in nessesary moment?
3)  (Extra) The last version refuse to combine several gro files in one trj file (previously it worked with gmx trjcat -cat -f {0..10}.gro -o traj.trr). How it to do now?






More information about the gromacs.org_gmx-users mailing list