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