[CP2K-user] [CP2K:20947] Energy from restart file not equal to energy at the end of geo opt

[Jürg Hutter]

Hi

this is due to the very loose accuracy/convergence settings in this example.
In the final calculation an additional SCF step is perfomed (the first energy
is the same as  at the end of the geometry optimization).
This single SCF step decreases the energy by another 10^-5 au.
Tighter settings (e.g. EPS_SCF 10^-7) will decrease this difference.

regards
JH

________________________________________
From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Bram Van der Linden <bramvdlinden98 at gmail.com>
Sent: Thursday, December 5, 2024 12:43 AM
To: cp2k
Subject: [CP2K:20945] Energy from restart file not equal to energy at the end of geo opt

Dear all,

I was following this tutorial: Geometry Optimisation — CP2K documentation<https://manual.cp2k.org/trunk/methods/optimization/geometry.html>
If I perform the geo opt, I get the snippet below at the end of the output file.
If I do an energy calculation from the restart file, I obtain that
ENERGY| Total FORCE_EVAL ( QS ) energy [a.u.]:              -17.164620477328342a
So, the energy of the energy calculation is equal to the energy at the last step (11), it is not equal to the energy that is recomputed after the last geometry optimization step.
Could someone explain why this is the case?
Many thanks in advance!
Bram

--------  Informations at step =    11 ------------
  Optimization Method        =                   SD
  Total Energy               =       -17.1646204773
  Real energy change         =        -0.0000000529
  Decrease in energy         =                  YES
  Used time                  =                2.886

  Convergence check :
  Max. step size             =         0.0003393777
  Conv. limit for step size  =         0.0010000000
  Convergence in step size   =                  YES
  RMS step size              =         0.0001493511
  Conv. limit for RMS step   =         0.0010000000
  Convergence in RMS step    =                  YES
  Max. gradient              =         0.0001787811
  Conv. limit for gradients  =         0.0010000000
  Conv. in gradients         =                  YES
  RMS gradient               =         0.0000786768
  Conv. limit for RMS grad.  =         0.0010000000
  Conv. in RMS gradients     =                  YES
 ---------------------------------------------------

 *******************************************************************************
 ***                    GEOMETRY OPTIMIZATION COMPLETED                      ***
 *******************************************************************************

                    Reevaluating energy at the minimum

 Number of electrons:                                                          8
 Number of occupied orbitals:                                                  4
 Number of molecular orbitals:                                                 4

 Number of orbital functions:                                                 23
 Number of independent orbital functions:                                     23

 Extrapolation method: ASPC


 SCF WAVEFUNCTION OPTIMIZATION

  Step     Update method      Time    Convergence         Total energy    Change
  ------------------------------------------------------------------------------
     1 Pulay/Diag. 0.50E+00    0.0     0.00005610       -17.1646204769 -1.72E+01
     2 Pulay/Diag. 0.50E+00    0.1     0.00000563       -17.1646347273 -1.43E-05

  *** SCF run converged in     2 steps ***


  Electronic density on regular grids:         -8.0000016293       -0.0000016293
  Core density on regular grids:                7.9999992519       -0.0000007481
  Total charge density on r-space grids:       -0.0000023775
  Total charge density g-space grids:          -0.0000023775

  Overlap energy of the core charge distribution:               0.00000004555422
  Self energy of the core charge distribution:                -43.83289054591484
  Core Hamiltonian energy:                                     12.82175609863938
  Hartree energy:                                              17.97395116248504
  Exchange-correlation energy:                                 -4.12745148803461

  Total energy:                                               -17.16463472727081

 ENERGY| Total FORCE_EVAL ( QS ) energy [a.u.]:              -17.164634727270808

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