# [gmx-developers] [Fwd: coulomb SR in 3.3cvs]

Michel Cuendet michel.cuendet at epfl.ch
Tue Jul 19 15:14:07 CEST 2005

```Hi David,

>You should only compare the first step. The virial (pressure) will tell
>you whether forces are correct.
>
Allright, here it is :

-------------------------------------------------------------------------
First step:  Virial XX, YY, ZZ, EKin, Pressure :
3.2.1 :
0.000000  68261.312500  75314.625000  68934.000000   216638.687500
44.703457
3.3 :
0.000000  68055.515625  75127.718750  69873.421875   218547.906250
75.353340

-------------------------------------------------------------------------
Energies at first step :
@ s0 legend "G96Bond"
@ s1 legend "G96Angle"
@ s2 legend "Proper Dih."
@ s3 legend "Improper Dih."
@ s4 legend "LJ-14"
@ s5 legend "Coulomb-14"
@ s6 legend "LJ (SR)"
@ s7 legend "Coulomb (SR)"
@ s8 legend "Coul. recip."
@ s9 legend "Potential"

3.2.1  :
0.000000  6909.100586  10166.941406  4475.063477  3269.806641
820.055969  62880.343750  166514.671875  -1203442.750000
-188707.640625  -1137114.375000
3.3 :
0.000000  6909.088867  10166.948242  4475.061523  3269.804443
820.041321  62880.359375  166517.578125  -1203541.000000
-188709.156250  -1137211.375000
-------------------------------------------------------------------------

We see that the energies are all accurate at least up to the 5th digit
(can we expect more frome single precision?). The virials diverge
already from the third digit. So do the kinetic energies, and the
pressures differ...

I don't know what conclusions to draw from that.

--
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Michel Cuendet, Ph.D. student
Laboratory of Computational Biochemistry and Chemistry
Swiss Federal Institute of Technology in Lausanne (EPFL)
CH-1015 Lausanne
Switzerland                         	Phone : +41 1 693 0324
lcbcpc21.epfl.ch/~mitch                        +41  1 633 4194
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

```