stress/atom

Hi,

I want to print the stress or pressure of a single atom into a file. When I put the following lines in the input script, no error occurs:

compute stress all stress/atom
variable xx equal c_stress[1][1]

However, trying to print the xx stress component of atom 1:

fix print all print 100 "${xx}" file xx.txt

results in the following error:

ERROR: Per-atom virial was not tallied on needed timestep

I don't understand this ERROR message even after refering to the LAMMPS documentation.

Best regards
Thomas Wagner.

PS: I found a solution in the forum:

1.) compute the total pressure:

compute as all stress/atom
compute p all reduce sum c_as[1] c_as[2] c_as[3]
variable press equal -(c_p[1]+c_p[2]+c_p[3])/(3*vol)

2.) thermo output the pressure:

thermo 100
thermo_style custom step atoms ke f_ts[1] f_ts[2] vol v_press
thermo_modify lost ignore norm no