Stress tensor units in VASP
Posted: Sat Jan 23, 2021 1:22 am
Hi,
Using ISIF = 2, I see the stress tensor shown below in OUTCAR. The units are in kB.
I am trying to calculate the viscosity from the autocorrelation of the stress tensors but I am a bit confused about the units. How do I convert the units to force/area correctly? Do I just use the area as the 19 A by 19 A from simulation cell domain of (19 by 19 by 19 A) and divide them myself? I am new to VASP so any detailed replies will be very helpful!
FORCE on cell =-STRESS in cart. coord. units (eV):
Direction XX YY ZZ XY YZ ZX
--------------------------------------------------------------------------------------
Alpha Z 3337.27325 3337.27325 3337.27325
Ewald -13766.64398-13378.95460-12267.70626 394.53466 313.37856 -411.30460
Hartree 4460.49785 4584.62850 5376.77117 228.27932 169.74402 -297.23216
E(xc) -5556.75762 -5554.11176 -5550.36199 1.63334 1.65833 -1.51841
Local -5261.77220 -5716.82918 -7575.62141 -597.73557 -459.36174 680.91225
n-local 1528.58188 1536.92086 1539.29470 4.19145 2.83248 -4.47476
augment 575.38997 578.42817 580.80399 1.23329 1.29091 -1.45153
Kinetic 14672.07661 14616.03617 14552.63714 -29.37575 -38.67712 38.64452
Fock 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000
-------------------------------------------------------------------------------------
Total -11.35425 3.39142 -6.90940 2.76076 -9.13455 3.57532
in kB -2.28664 0.68300 -1.39149 0.55599 -1.83962 0.72004
external pressure = -1.00 kB Pullay stress = 0.00 kB
Using ISIF = 2, I see the stress tensor shown below in OUTCAR. The units are in kB.
I am trying to calculate the viscosity from the autocorrelation of the stress tensors but I am a bit confused about the units. How do I convert the units to force/area correctly? Do I just use the area as the 19 A by 19 A from simulation cell domain of (19 by 19 by 19 A) and divide them myself? I am new to VASP so any detailed replies will be very helpful!
FORCE on cell =-STRESS in cart. coord. units (eV):
Direction XX YY ZZ XY YZ ZX
--------------------------------------------------------------------------------------
Alpha Z 3337.27325 3337.27325 3337.27325
Ewald -13766.64398-13378.95460-12267.70626 394.53466 313.37856 -411.30460
Hartree 4460.49785 4584.62850 5376.77117 228.27932 169.74402 -297.23216
E(xc) -5556.75762 -5554.11176 -5550.36199 1.63334 1.65833 -1.51841
Local -5261.77220 -5716.82918 -7575.62141 -597.73557 -459.36174 680.91225
n-local 1528.58188 1536.92086 1539.29470 4.19145 2.83248 -4.47476
augment 575.38997 578.42817 580.80399 1.23329 1.29091 -1.45153
Kinetic 14672.07661 14616.03617 14552.63714 -29.37575 -38.67712 38.64452
Fock 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000
-------------------------------------------------------------------------------------
Total -11.35425 3.39142 -6.90940 2.76076 -9.13455 3.57532
in kB -2.28664 0.68300 -1.39149 0.55599 -1.83962 0.72004
external pressure = -1.00 kB Pullay stress = 0.00 kB