[Pw_forum] A little question about total energy

Paolo Giannozzi giannozz at nest.sns.it
Fri May 16 15:28:49 CEST 2003


>    In the output of PWSCF, the energy partitions are list
> following the total energy as I pasted below. I found
> that the total energy is not equal to the sum of those listed
> partitions.

Total Energy = sum of terms marked with "+" below =
    one-electron + hartree + xc + ewald + correction for metals

!    total energy              =   -62.07569469 ryd
     estimated scf accuracy    <     0.00000799 ryd

     band energy sum           =   -14.82580512 ryd
+    one-electron contribution =   -98.79712762 ryd
+    hartree contribution      =    51.10053218 ryd
+    xc contribution           =   -14.02297161 ryd
+    ewald contribution        =    -0.34484385 ryd
      scf in/out correction     =     0.02901784 ryd
+    correction for metals     =    -0.01128379 ryd

The "one-electron contribution" is the kinetic + ionic term:
  \sum <psi| T + V_ion | psi>
The "band energy sum" is exactly what it claims to be:
  \sum epsilon = \sum <psi| T + V_ion + V_scf | psi>
The "correction for metals" makes forces and energies 
consistent if a broadening scheme is used.
The "scf in/out correction" is no longer used
(and no longer useful)
The "estimated scf accuracy" gives an estimate of the 
error on the energy due to imperfect self-consistency.

Admittedly, it is slightly confusing.


Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050509412
Piazza dei Cavalieri 7      Fax:     +39/050509417, 050563513     
I-56126 Pisa, Italy         Office:  Lab. NEST, Via della Faggiola 19

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