### Total Energy from Density of States

Posted:

**Wed Nov 08, 2017 3:57 pm**Hallo all, I really hope somebody can help me with my issue.

I have been trying to obtain the total energy of a system from the total density of states. However, prior of doing so I have been reproducing some simple DOS for single atoms like Al or molecules like CO successfully from the literature. So, my plots look like the one in the literature.

Now I tried to integrate the total DOS with respect to the energy (see the attached formula), but always failed to obtain the energy given in the vasp.log or OUTCAR file.

In a second attempt, I investigated two cases:

1. Fully optimised system with a metal atom adsorbed to a graphene sheet.

2. Graphene sheet with the metal atom 10 or 20 Ang away.

I was expecting that there are no interactions between the metal atom and the graphene sheet, and there should not be any. Thus the energy difference of both systems should be close the binding energy. While this worked nicely comparing the total energies from the OUTCAR, obtaining the total energy via integration of the total DOS gave a difference of roughly 50, in some cases even 100eV.

Now my questions after this long introduction:

1. Is it possible to obtain the energy given in the OUTCAR of the system by integrating over the total DOS? If so, how can I do this? If not, what is the reason for this?

2. If it is possible, does the same method work for the pDOS as well?

In case it helps, below are the parameters I used in the INCAR when computing for the DOS:

System = DOS_test_runs

ENCUT = 450

PREC = High

EDIFF = 1E-9

ISTART = 0

ICHARG = 11

EDIFFG = -0.01

NSW = 0

ISIF = 2

ISMEAR = -5 or 0 when calculating for isolated atoms

SIGMA = 0.1

ISPIN = 2 or 1 in case of closed shell systems

EMIN = -25

EMAX = 10

LORBIT = 10

NEDOS = 5001

NPAR = 1

IBRION = -1

I really hope you can help me with this.

I have been trying to obtain the total energy of a system from the total density of states. However, prior of doing so I have been reproducing some simple DOS for single atoms like Al or molecules like CO successfully from the literature. So, my plots look like the one in the literature.

Now I tried to integrate the total DOS with respect to the energy (see the attached formula), but always failed to obtain the energy given in the vasp.log or OUTCAR file.

In a second attempt, I investigated two cases:

1. Fully optimised system with a metal atom adsorbed to a graphene sheet.

2. Graphene sheet with the metal atom 10 or 20 Ang away.

I was expecting that there are no interactions between the metal atom and the graphene sheet, and there should not be any. Thus the energy difference of both systems should be close the binding energy. While this worked nicely comparing the total energies from the OUTCAR, obtaining the total energy via integration of the total DOS gave a difference of roughly 50, in some cases even 100eV.

Now my questions after this long introduction:

1. Is it possible to obtain the energy given in the OUTCAR of the system by integrating over the total DOS? If so, how can I do this? If not, what is the reason for this?

2. If it is possible, does the same method work for the pDOS as well?

In case it helps, below are the parameters I used in the INCAR when computing for the DOS:

System = DOS_test_runs

ENCUT = 450

PREC = High

EDIFF = 1E-9

ISTART = 0

ICHARG = 11

EDIFFG = -0.01

NSW = 0

ISIF = 2

ISMEAR = -5 or 0 when calculating for isolated atoms

SIGMA = 0.1

ISPIN = 2 or 1 in case of closed shell systems

EMIN = -25

EMAX = 10

LORBIT = 10

NEDOS = 5001

NPAR = 1

IBRION = -1

I really hope you can help me with this.