# [lammps-users] GK method using Virial stress

``````Hi all, I've searched the email list archive and found this long discussion on calculating thermal conductivity using GK
method. Can someone explain to me why the Virial part was divided by 1.6021765e6, since the unit for each system is consistent,

including metal and real. What I dont know is the unit of Virial stress. Should it be the same as pressure*volume (so should be bar*A^3 if it is in metal unit)?

Steve may want to answer this.

Thanks, Ajing

>> compute        PE all pe/atom
>> compute        KE all ke/atom
>>

>> variable       CX atom (vx[]*(c_KE[]+c_PE[]))
>> compute        Jcx all reduce sum v_CX
>>
>> variable       CY atom (vy[]*(c_KE[]+c_PE[]))
>> compute        Jcy all reduce sum v_CY

>>
>> variable       CZ atom (vz[]*(c_KE[]+c_PE[]))
>> compute        Jcz all reduce sum v_CZ
>>
>> compute        SA all stress/atom virial
>>
>> # J_x = S_xx*V_x + S_xy*V_y + S_xz*V_z

>> variable       VX atom
>> -(c_SA[]*vx[]+c_SA[]*vy[]+c_SA[]*vz[])/1.6021765e6
>> compute        Jvx all reduce sum v_VX
>> # J_y = S_yx*V_x + S_yy*V_y + S_yz*V_z, yx=xy
>> variable       VY atom

>> -(c_SA[]*vx[]+c_SA[]*vy[]+c_SA[]*vz[])/1.6021765e6
>> compute        Jvy all reduce sum v_VY
>> # J_z = S_zx*V_x + S_zy*V_y + S_zz*V_z, yx=xy
>> variable       VZ atom
>> -(c_SA[]*vx[]+c_SA[]*vy[]+c_SA[]*vz[])/1.6021765e6

>> compute        Jvz all reduce sum v_VZ
>>
>> variable       Jx equal (c_Jcx+c_Jvx)
>> variable       Jy equal (c_Jcy+c_Jvy)
>> variable       Jz equal (c_Jcz+c_Jvz)
``````

Can someone explain to me why the Virial part was divided by 1.6021765e6, since the unit for each system >is consistent, including metal and real. What I dont know is the unit of Virial stress. Should it be the same >as pressure*volume (so should be bar*A^3 if it is in metal unit)?

Real and metal units are not consistent, meaning you can not take any
2 quantities and
multiply them and get the same units as another quantity. Hence you often
need conversion factors. The units produced by any compute are
stated explicitly on the doc page for that compute.

Steve