Error when doing MD with freezing partial of atoms

[pxlxingliang]

Describe the Bug

when doing MD with freezing partial of atoms, some values (like NVT Conservation/NVT Kinetic energy) are "-nan"

mderror.zip

INPUT:
INPUT_PARAMETERS
#Parameters (General)
suffix autotest
ntype 1
nbands 8
calculation md
#Parameters (Accuracy)
ecutwfc 20
niter 50
dr2 1.0e-8
basis_type pw
nstep 4
stress 1
stress_thr 1e-6
force 1
force_thr_ev 1.0e-3
mixing_type pulay
mixing_beta 0.7
charge_extrap first-order

STRU:
ATOMIC_POSITIONS
Cartesian #Cartesian(Unit is LATTICE_CONSTANT)
Si #Name of element
0.0 #Magnetic for this element.
2 #Number of atoms
0.00 0.00 0.00 0 0 0 #x,y,z, move_x, move_y, move_z
0.25 0.25 0.25 1 1 1

running_md.log
...

Molecular Dynamics (NVT) STEP 1

---

        SUMMARY OF NVT CALCULATION

---

NVT Conservation : -nan (Rydberg)
NVT Temperature : -nan (K)
NVT Kinetic energy : -nan (Rydberg)
NVT Potential energy : -15.567031 (Rydberg)
maxForce : +0.000000
maxStep : +0.000000
...

output:
...
notconv = 8
Hamilt::diago', too many bands are not converged!

notconv = 8
Hamilt::diago', too many bands are not converged!
...

[mohanchen]

@YuLiu98 could you please check this problem?

[YuLiu98]

Due to the fixed mass center and one fixed atom, the total freedom of the system (2 atoms in total) is zero, which is used as denominator in the calculation of temperature, resulting in the presence of the error.

[YuLiu98]

There are some alternative solutions:

1. Quit out when the freedom is zero.
2. When no atom is fixed, the mass center is set to be fixed, otherwise the mass center is unfixed.