[CP2K:10764] Why doesn't the Cons Qty include the potential energy of shell (shell model) in NVE ensemble?

[Krack Matthias (PSI)]

Dear Zuoheng

Though the regression test inputs may serve as a kind of initial input template for an application case, the settings for these tests are rather sloppy allowing for a quick processing in order to check a specific program feature or functionality. The core-shell model requires smaller time steps than rigid-ion force fields because of the usually faster motion of the light shell particles. At ambient conditions 0.5 fs might be a good guess, but smaller and smaller time steps are required for increasing temperatures until the break-down of the approach (“polarisation catastrophe”) at high temperatures will occur. The shell particles should always stay close to their core particles. Core-shell distances of more than 0.5A indicate that the approach is going to break-down.
There is the option to minimise (relax) the core-shell distances (MOTION/SHELL_OPT<https://manual.cp2k.org/trunk/CP2K_INPUT/MOTION/SHELL_OPT.html> section) if you specify for MAX_DISTANCE a value greater that zero and that value is surpassed. That is useful for initialisation or structure optimisation runs, but the energy conservation is affected when such relaxation steps are randomly performed during an MD run. MAX_DISTANCE has only an effect if the SHELL_OPT section is explicitly specified.

HTH

Matthias

From: cp... at googlegroups.com <cp... at googlegroups.com> On Behalf Of zuohen... at gmail.com
Sent: Donnerstag, 20. September 2018 10:10
To: cp2k <cp... at googlegroups.com>
Subject: Re: [CP2K:10764] Why doesn't the Cons Qty include the potential energy of shell (shell model) in NVE ensemble?

Dear Matthias,

Thank you for your reply.
Could I ask an another question?
I found core-shell model should use a smaller time step (0.1 - 0.2fs). However the time step of some U2O simulation in cp2k test files is larger (0.5fs even 1fs).
Is it because you use a heavier shell mass (MASS_FRACTION of O is 0.1) [1] and use a MAX_DISTANCE = 0.5 angstrom?
How do I determine the MAX_DISTANCE in my simulation of O2- and OH- ions with shell model?

Thank you very much~

Best wishes,
Zuoheng

[1] Devynck F, Iannuzzi M, Krack M. Frenkel pair recombinations in UO 2: importance of explicit description of polarizability in core-shell molecular dynamics simulations. Physical Review B, 2012, 85(18): 184103.

在 2018年9月19日星期三 UTC+2下午7:55:28，Matthias Krack写道：
Dear Zuoheng

md_ener%epot contains the potential energy of all particles including the shell particles.

Best regards

Matthias

Von: cp... at googlegroups.com<javascript:> <cp... at googlegroups.com<javascript:>> Im Auftrag von zuoh... at gmail.com<javascript:>
Gesendet: Mittwoch, 19. September 2018 17:15
An: cp2k <cp... at googlegroups.com<javascript:>>
Betreff: [CP2K:10755] Why doesn't the Cons Qty include the potential energy of shell (shell model) in NVE ensemble?

Dear CP2K developers,

I am sorry to disturb you. I have some questions.
Recently I want to analyze whether the total energy is converged with core-shell model in NVE ensemble. I didn't use extra thermostat for shell.
I don't know why the Cons Qty energy = md_ener%ekin+md_ener%epot+md_ener%ekin_shell but not including the potential of shell? Is the Cons Qty the total energy? In NVE ensemble, which energy should be constant? ekin+epot+ekin_shell+epot_shell or ekin+epot+ekin_shell?

Thank you very much~

Best wishes,
Zuoheng

PS:The whole code of get_econs_nve function is following:
SUBROUTINE get_econs_nve(md_env, md_ener, para_env)
      TYPE(md_environment_type), POINTER                 :: md_env
      TYPE(md_ener_type), INTENT(inout)                  :: md_ener
      TYPE(cp_para_env_type), POINTER                    :: para_env

      CHARACTER(LEN=*), PARAMETER :: routineN = 'get_econs_nve', routineP = moduleN//':'//routineN

      TYPE(force_env_type), POINTER                      :: force_env
      TYPE(thermostat_type), POINTER                     :: thermostat_coeff, thermostat_shell

      NULLIFY (force_env, thermostat_coeff, thermostat_shell)

      CALL get_md_env(md_env, force_env=force_env, thermostat_coeff=thermostat_coeff, &
                      thermostat_shell=thermostat_shell)
      md_ener%constant = md_ener%ekin+md_ener%epot+md_ener%ekin_shell

      CALL get_thermostat_energies(thermostat_shell, md_ener%thermostat_shell_pot, &
                                   md_ener%thermostat_shell_kin, para_env)
      md_ener%constant = md_ener%constant+md_ener%thermostat_shell_kin+md_ener%thermostat_shell_pot

   END SUBROUTINE get_econs_nve

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