Do not fix NH during NVT melting

[pmrv]

I get this error when I try to run a liquid TS calculation in NVT, i.e. pressure=None. I think this PR should fix it, but I haven't tested it.

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/u/zora/software/pyiron_base/pyiron_base/cli/__main__.py", line 3, in <module>
    main()
  File "/u/zora/software/pyiron_base/pyiron_base/cli/control.py", line 61, in main
    args.cli(args)
  File "/u/zora/software/pyiron_base/pyiron_base/cli/wrapper.py", line 37, in main
    job_wrapper_function(
  File "/u/zora/software/pyiron_base/pyiron_base/jobs/job/wrapper.py", line 186, in job_wrapper_function
    job.run()
  File "/u/zora/software/pyiron_base/pyiron_base/jobs/job/wrapper.py", line 131, in run
    self.job.run_static()
  File "/u/zora/software/pyiron_atomistics/pyiron_atomistics/calphy/job.py", line 712, in run_static
    routine_ts(job)
  File "/cmmc/ptmp/zora/software/calphy/calphy/routines.py", line 347, in routine_ts
    routine_fe(job)
  File "/cmmc/ptmp/zora/software/calphy/calphy/routines.py", line 328, in routine_fe
    job.run_averaging()
  File "/cmmc/ptmp/zora/software/calphy/calphy/liquid.py", line 137, in run_averaging
    self.melt_structure(lmp)
  File "/cmmc/ptmp/zora/software/calphy/calphy/liquid.py", line 72, in melt_structure
    self.fix_nose_hoover(lmp, temp_start_factor=factor, temp_end_factor=factor)
  File "/cmmc/ptmp/zora/software/calphy/calphy/phase.py", line 267, in fix_nose_hoover
    self.iso, press_start_factor*self.calc._pressure, press_end_factor*self.calc._pressure, self.calc.md.barostat_damping[stage]))
              ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
TypeError: unsupported operand type(s) for *: 'float' and 'NoneType'

This was my input.yml

calculations:
- berendsen:
    barostat_damping: 100.0
    thermostat_damping: 100.0
  element:
  - Mg
  equilibration_control: nose-hoover
  fix_potential_path: false
  lattice: /cmmc/u/zora/pyiron/projects/2024/06_MTP_Mg_pT_Phasediagram/Mg/CALPHY/liquid_15d0_hdf5/liquid_15d0/conf.data
  mass:
  - 24.305
  md:
    barostat_damping: 0.1
    n_cycles: 100
    n_every_steps: 10
    n_repeat_steps: 10
    n_small_steps: 10000
    thermostat_damping: 0.5
    timestep: 0.001
  melting_cycle: true
  mode: ts
  n_equilibration_steps: 25000
  n_iterations: 1
  n_print_steps: 0
  n_switching_steps: 50000
  nose_hoover:
    barostat_damping: 0.1
    thermostat_damping: 0.1
  npt: false
  pair_coeff:
  - '* *'
  pair_style:
  - mlip mlip.ini
  pressure: null
  queue:
    cores: 80
  reference_phase: liquid
  spring_constants: null
  temperature:
  - 2749.999999999982
  - 3499.999999999982
  tolerance:
    lattice_constant: 0.0002
    liquid_fraction: 0.05
    pressure: 0.5
    solid_fraction: 0
    spring_constant: 0.01

[pmrv]

@srmnitc Turns out melting_cycle=True is not sufficient, because of this line, that always tries to a p=0 equilibration but then fails when no pressure is specified. In solids there is instead a check that seems to work around this. You think it would be enough to just copy this to liquids?

[srmnitc]

work in progress over at #135

[srmnitc]

should be fixed now in #135 , im gonna go ahead and close this