[gmx-users] a question about output virial

[Lu Lanyuan]

Hello,
>From the mailinglist archive It is said the scalar virial from the g_energy
vir=(1/3)*(vir(xx)+vir(yy)+vir(zz))=-0.5*sum(i<j)(F(ij)*r(ij)), if 
interactions are pairwised.
I tried to verify this by using the relation 
PV=(2/3)*E(kin)+(1/3)*sum(i<j)(F(ij)*r(ij)).
All instantaneous virial, kinetic energy, pressure and volume can be 
obtained from g_energy.
But I found the scalar virial I got using the first equation need to be 
multiplied by 3 to satisfy the second equation. That is to say, vir is 
actually -0.5*(1/3)*sum(i<j)(F(ij)*r(ij)) if I use the definition 
vir=(1/3)*(vir(xx)+vir(yy)+vir(zz)).
Can anyone give any comments about this?
Thanks!
Lanyuan Lu

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