# H2 molecule : study of translational and rotational modes
ndtset 3
ecut 12.0
ecutsm 1.0
ixc 1
ngkpt 2 2 2 !! Better to use this than the gamma point
diemac 2
nband 1
### First data set : geometry optimization
kptopt1 1
tolmxf1 1.0d-5
ntime1 10
toldff1 1.0d-6
ionmov1 3
### Second data set : accurate wave function calculation ###
kptopt2 1
tolwfr2 1.0d-22
getwfk2 -1
getxcart2 -1
### Third data set : atomic displacement ###
kptopt3 2
nqpt3 1
qpt3 0.0 0.0 0.0
rfphon3 1
rfatpol3 1 2
rfdir3 1 1 1
tolvrs3 1.0d-9
getwfk3 -1
getxcart3 -2
### Structure parameters ###
acell 3*14.0
natom 2
nstep 40
xcart 7.2669124276E-01 0.0000000000E+00 0.0000000000E+00
-7.2669124276E-01 0.0000000000E+00 0.0000000000E+00
ntypat 1
typat 1 1
znucl 1.00
## After modifying the following section, one might need to regenerate the pickle database with runtests.py -r
#%%
#%% [setup]
#%% executable = abinit
#%% [files]
#%% files_to_test =
#%% t80.out, tolnlines = 0, tolabs = 1.289e-10, tolrel = 3.000e-10, fld_options = -medium
#%% psp_files = 01h.pspgth
#%% [paral_info]
#%% max_nprocs = 1
#%% [extra_info]
#%% authors = Unknown
#%% keywords = NC, DFPT
#%% description =
#%% H2 molecule : examine the rotational freedom.
#%% The present test produces the following
#%% vibrational frequencies (with degeneracies indicated):
#%% 56.89 i cm-1 (2)
#%% 0.41 cm-1 (2)
#%% 1.05 cm-1
#%% 3800 cm-1
#%% The large frequency corresponds to the stretching
#%% mode, and has the right order of magnitude.
#%% The frequencies close to 1 cm-1 corresponds
#%% to translation modes, and are small enough
#%% for usual applications.
#%% The 56.89 i cm-1 mode corresponds to rotation of
#%% the H2 molecule. The magnitude of this
#%% frequency might seem quite
#%% large. Here are the results of tests made to understand
#%% this phenomenon. First, note that
#%% ecut 12 acell 3*14
#%% Increasing the value of ecut to 25 decreases
#%% the magnitude of the frequency to 36.8 cm-1 .
#%% However, in order to continue to make it smaller,
#%% the cell size must be increased , and an oscillatory
#%% behaviour is observed :
#%% 3*16 45.6 i cm-1
#%% 3*18 22.7 cm-1
#%% 3*20 19.1 i cm-1
#%% 3*22 15.7 i cm-1
#%% 3*24 13.7 cm-1
#%% Many other tests have been set up. In particular,
#%% it was observed that the frequency of the oscillatory
#%% behaviour changes with the ecut, and also that
#%% using the Gamma point, instead of the 1/4 1/4 1/4 k point
#%% (used in this test) degrades the convergence.
#%% The overall picture is as follows.
#%% There are different reasons for the translation
#%% and rotation modes to acquire a non-zero frequency
#%% when plane waves and supercells are used.
#%% Still, as concerns translations, only the
#%% existence of a discretization of the XC grid
#%% is important. For rotations, supercell effects
#%% are also present :
#%% - alignement of dipole or quadrupoles
#%% - interaction between tails of wavefunctions, accross cells
#%% Since the convergence in supercell size is oscillatory, we infer
#%% that the breaking of the rotational invariance is mostly
#%% due to interaction between wavefunction tails.
#%% This will be checked by confining the system in a spherical
#%% well, in a forthcoming test.
#%%