Hello!
First, total energy is not a conserved quantity in the NV
T ensemble! Some thermostats, like the Nosé-Hoover thermostat, provide a "pseudo-Hamiltonian", i.e. a similar conserved quantity, which one can check for conservation even in the case of an NVT simulation. However, I am not aware that this is possible with the Langevin thermostat.
In case you want to use the Langevin thermostat, you can only check energy conservation by setting
LANGEVIN_GAMMA to zero, which actually disables the thermostat and results in an NV
E simulation. Then, the conserved energy is provided in the following ways:
(1)
OSZICAR: In the line
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1 T= 295. E= -.40126502E+02 F= -.40431392E+02 E0= -.40431392E+02 EK= 0.30489E+00 SP= 0.00E+00 SK= 0.00E+00
corresponds to the conserved total energy, which is the sum
E = F + EK (actually
+ SP + SK, but these terms are zero for the Langevin thermostat).
(2)
OUTCAR: In the sections
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FREE ENERGIE OF THE ION-ELECTRON SYSTEM (eV)
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free energy TOTEN = -40.43139170 eV
energy without entropy= -40.43139170 energy(sigma->0) = -40.43139170
and
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ENERGY OF THE ELECTRON-ION-THERMOSTAT SYSTEM (eV)
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% ion-electron TOTEN = -40.431392 see above
kinetic energy EKIN = 0.304889
kin. lattice EKIN_LAT= 0.000000 (temperature 294.84 K)
nose potential ES = 0.000000
nose kinetic EPS = 0.000000
---------------------------------------------------
total energy ETOTAL = -40.126502 eV
is the conserved energy which is the sum
ETOTAL = TOTEN + EKIN (actually
+ EKIN_LAT + ES + EPS, but these terms are again all zero here).
Often, if one is only interested in single-structure energies, the energy
E0 (
energy(sigma->0) = ...) is reported as potential energy. However, the potential energy surface corresponding to the analytic forces provided by VASP is given by
F (
TOTEN). Usually, the difference is tiny, it depends on the smearing parameter
ISMEAR.
Best,
Andreas Singraber