[SPAM] unexpected energy change

Dear lammps-user,
I calculated the velocity of an iron atom correspondant to an energy of 1keV, and tried to verify the result through thermo output, however the total energy change was not 1keV but 8.1keV. I’m quite sure the velocity I put in the in file is correct, so I wonder where is the error.
The in file is as followed:

Dear lammps-user,
I just checked the velocity of group pka and found that its velocity was 1677.89 instead of 587. What happened?
Thanks in advance.

Philip

------------------ Original ------------------

Dear lammps-user,
I calculated the velocity of an iron atom correspondant to an energy of
1keV, and tried to verify the result through thermo output, however the
total energy change was not 1keV but 8.1keV. I'm quite sure the velocity I
put in the in file is correct, so I wonder where is the error.

because you made additional modifications to the total energy with
these two commands:

velocity all zero linear
velocity all zero angular

axel.

Dear lammps-user,
I calculated the velocity of an iron atom correspondant to an energy of
1keV, and tried to verify the result through thermo output, however the
total energy change was not 1keV but 8.1keV. I'm quite sure the velocity I
put in the in file is correct, so I wonder where is the error.

because you made additional modifications to the total energy with
these two commands:

velocity all zero linear
velocity all zero angular

upon closer inspection of your input and the documentation, there are
two additional issues:

you use velocity create and then velocity set without the "sum yes"
flag. that means that you remove the preexisting energy for atoms in
the group pka.

even more significant, however, is the fact that you are using the
default settings for "units", which is "lattice" and thus your input
velocities are scaled by the respective lattice spacing (2.859) and
2.859**2 is about 8.2.

so to get the expected energy added you'd have to add the flags "sum
yes units box" to your velocity set command.

it is all described in the documentation for the velocity command.
please have another look.

axel.