According to Equipartition theorem, temperature is calculated from the sum of X.Y and Z kinetic energy, so temperature should have X Y and Z three components. Assume my system has reached thermal equilibrium state at 50K. Now I want to increase the X component of temperature to 200K without doing anything to Y and Z temperature components, which means Y and Z temperatures will increase just because X temperature component transfers energy to them. I didn’t find any command in the manual about how to do this. I really appreciate it if anyone could tell me how to realize this. Thanks.

Hi,
According to Equipartition theorem, temperature is calculated from the sum
of X.Y and Z kinetic energy, so temperature should have X Y and Z three
components. Assume my system has reached thermal equilibrium state at 50K.
Now I want to increase the X component of temperature to 200K without doing
anything to Y and Z temperature components, which means Y and Z temperatures
will increase just because X temperature component transfers energy to
them. I didn't find any command in the manual about how to do this. I really
appreciate it if anyone could tell me how to realize this. Thanks.

how about this?

variable fourvx atom 4*vx
velocity all v_fourvx NULL NULL sum no

If you want to apply a thermostat only to the x degree of freedom of
your atoms, you can bias the thermostat by combining it with compute
temp/partial, something like:

compute newT all temp/partial 1 0 0
fix 1 all nvt temp 200.0 200.0 100.0
fix_modify 1 temp newT