[CP2K:2654] Looking for zero frequencies
Teodoro Laino
teodor... at gmail.com
Fri Apr 9 15:37:18 UTC 2010
Dear An,
did you try to use a smaller DX (in the VIB section): the hessian is
computed numerically and 0.01 may definitely be too large.
Teo
An Ghysels wrote:
> Dear forum users,
>
> I am calculating frequencies in periodic structures, from which I'd
> like to derive thermodynamic quantities like the entropy etc.
> Therefore I use the VIBRATIONAL_ANALYSIS keyword, where I have put the
> FULLY_PERIODIC keyword to True, such that rotational motions are not
> projected out.
>
> In principle, the second derivatives matrix should have 3 zero
> eigenvalues (even in non-optimized systems), because the system is
> translational invariant. However, this is not the case in my
> calculations. Even in a small test case like diamond with a cubic cell
> containing 8 atoms, the "zero" frequencies deviate largely from zero.
>
> (Between brackets: I'm much bothered by this bad performance, because
> it signals that the numerical accuracy of the frequencies is poor. I
> aim at studying larger unit cells (eg with 100 to 200 QM atoms) where
> I surely will encounter floppy modes, which are even more sensible to
> numerical errors. And those floppy modes play an essential role in the
> partition function/thermodynamics. Therefore, I wish to improve the
> accuracy of the calculated frequencies.)
>
> So my questions are mainly: why is the accuracy so bad? Is this
> directly related to the eggbox effect, and if so, how to remedy it? Is
> it something with interpolation grids? And what to do to improve it?
>
> I tried decreasing the EPS_DEFAULT (down to 10e-16), increasing the
> E_CUTOFF (up to 1400 Rydberg), increasing the REL_CUTOFF accordingly,
> adding the keyword COMMENSURATE, changing the interpolation grid (to
> spline3), but the improvements still do not get me close to "zero"
> frequencies (still of the order -70 to 50 cm-1).
>
> Looking forward to your comments and remarks,
>
> An
>
> Below: Information on version, input geometry optimization, input
> frequency run, snippets of output
> =====
> Version:
> CP2K| version string: CP2K version 2.0.1
> (Development Version)
> CP2K| is freely available from http://cp2k.berlios.de/
> CP2K| Program compiled at
> Wed_Sep__9_15:48:59_CEST_2009
> CP2K| Program compiled
> on gengar1
> CP2K| Program compiled for Linux-
> x86-64-intel
> =====
> Input geomery optimization
> &GLOBAL
> PRINT_LEVEL high
> PROJECT_NAME vib
> RUN_TYPE GEO_OPT
> PREFERRED_FFT_LIBRARY FFTW
> &END GLOBAL
>
> &MOTION
> &GEO_OPT
> OPTIMIZER BFGS
> MAX_ITER 300
> &END GEO_OPT
> &END MOTION
>
> &VIBRATIONAL_ANALYSIS
> FULLY_PERIODIC T
> &END VIBRATIONAL_ANALYSIS
>
> &FORCE_EVAL
>
> METHOD QS
> &DFT
> BASIS_SET_FILE_NAME GTH_BASIS_SETS
> POTENTIAL_FILE_NAME GTH_POTENTIALS
> &MGRID
> CUTOFF 100
> REL_CUTOFF 23
> COMMENSURATE
> &END MGRID
> &QS
> EPS_DEFAULT 1.0E-10
> &END QS
> &SCF
> EPS_SCF 1.0E-5
> MAX_SCF 100
> SCF_GUESS RESTART
> &OUTER_SCF
> EPS_SCF 1.0E-5
> MAX_SCF 20
> &END
> &OT
> ALGORITHM IRAC
> MINIMIZER CG
> PRECONDITIONER FULL_ALL
> ENERGY_GAP 0.001
> &END OT
> &PRINT
> &RESTART
> BACKUP_COPIES 0
> &END RESTART
> &END PRINT
> &END SCF
> &XC
> &XC_FUNCTIONAL PBE
> &END XC_FUNCTIONAL
> &END XC
> &POISSON
> POISSON_SOLVER PERIODIC
> PERIODIC XYZ
> &EWALD
> EWALD_TYPE EWALD
> ALPHA 0.3
> GMAX 11
> O_SPLINE 6
> &END EWALD
> &END POISSON
> &PRINT
> &END PRINT
> &END DFT
>
> &SUBSYS
> &CELL
> ABC 3.567 3.567 3.567
> PERIODIC XYZ
> &END CELL
> &COORD
> C -0.066491 -0.063731 -0.038851
> C 0.019572 1.759040 1.767428
> C 1.756129 0.023158 1.769616
> C 1.767376 1.770784 0.004363
> C 0.841267 0.843123 0.828198
> C 2.663349 0.903043 2.661920
> C 0.899007 2.665284 2.661387
> C 2.644659 2.648722 0.926362
> &END COORD
> &TOPOLOGY
> &GENERATE
> CREATE_MOLECULES
> &END GENERATE
> &END TOPOLOGY
>
> &KIND C
> BASIS_SET DZVP-GTH
> POTENTIAL GTH-PBE-q4
> &END KIND
>
> &END SUBSYS
> &END FORCE_EVAL
> =====
> Input Frequency run
> &GLOBAL
> PRINT_LEVEL high
> PROJECT_NAME vib
> RUN_TYPE VIBRATIONAL_ANALYSIS
> PREFERRED_FFT_LIBRARY FFTW
> &END GLOBAL
>
> &MOTION
> &GEO_OPT
> OPTIMIZER BFGS
> MAX_ITER 300
> &END GEO_OPT
> &END MOTION
>
> &VIBRATIONAL_ANALYSIS
> FULLY_PERIODIC T
> &END VIBRATIONAL_ANALYSIS
>
> &FORCE_EVAL
>
> METHOD QS
> &DFT
> BASIS_SET_FILE_NAME GTH_BASIS_SETS
> POTENTIAL_FILE_NAME GTH_POTENTIALS
> &MGRID
> CUTOFF 100
> REL_CUTOFF 23
> COMMENSURATE
> &END MGRID
> &QS
> EPS_DEFAULT 1.0E-10
> &END QS
> &SCF
> EPS_SCF 1.0E-5
> MAX_SCF 100
> SCF_GUESS RESTART
> &OUTER_SCF
> EPS_SCF 1.0E-5
> MAX_SCF 20
> &END
> &OT
> ALGORITHM IRAC
> MINIMIZER CG
> PRECONDITIONER FULL_ALL
> ENERGY_GAP 0.001
> &END OT
> &PRINT
> &RESTART
> BACKUP_COPIES 0
> &END RESTART
> &END PRINT
> &END SCF
> &XC
> &XC_FUNCTIONAL PBE
> &END XC_FUNCTIONAL
> &END XC
> &POISSON
> POISSON_SOLVER PERIODIC
> PERIODIC XYZ
> &EWALD
> EWALD_TYPE EWALD
> ALPHA 0.3
> GMAX 11
> O_SPLINE 6
> &END EWALD
> &END POISSON
> &PRINT
> &END PRINT
> &END DFT
> &SUBSYS
> &CELL
> ABC 3.567 3.567 3.567
> PERIODIC XYZ
> &END CELL
> &COORD
> C -0.0393192769 -0.0522499977 -0.0007602780
> C 0.0299677090 1.7769206120 1.7824574256
> C 1.7642084626 0.0471181783 1.7911208859
> C 1.7938452241 1.7853211459 0.0053883203
> C 0.8664406756 0.8762954420 0.8435833733
> C 2.6939879368 0.9029246308 2.6806928814
> C 0.9092781460 2.6785011492 2.6771532650
> C 2.6481574040 2.6661172907 0.9483093511
> &END COORD
> &TOPOLOGY
> &GENERATE
> CREATE_MOLECULES
> &END GENERATE
> &END TOPOLOGY
>
> &KIND C
> BASIS_SET DZVP-GTH
> POTENTIAL GTH-PBE-q4
> &END KIND
>
> &END SUBSYS
> &END FORCE_EVAL
> =====
> Snippet output frequency run:
> If I look at the values with the lowest absolute value and I convert
> them to cm-1, it is poor accuracy:
>
> VIB| Cartesian Low frequencies ----0.44072 -0.10876E-01
> 0.12458 0.69806
> VIB| Cartesian Low frequencies --- 0.71490 1.4715
> 2.0898 3.8120
> VIB| Cartesian Low frequencies --- 5.8007
> VIB| Frequencies after removal of the rotations and translations
> VIB| Internal Low frequencies ----0.14095 0.50894
> 1.4072 2.0559
> VIB| Internal Low frequencies --- 3.6794 5.7900
> 25.027 25.504
> VIB| Internal Low frequencies --- 25.855 25.997
> 26.180 26.684
> VIB| Internal Low frequencies --- 26.818 26.970
> 27.202 27.461
> VIB| Internal Low frequencies --- 27.643 28.937
> 54.059 54.351
> VIB| Internal Low frequencies --- 54.817
>
> VIB| NORMAL MODES - CARTESIAN DISPLACEMENTS
> VIB|
> VIB| 1
> 2 3
> VIB|Frequency (cm^-1) -82.399299 156.573040
> 260.352529
> ...
>
> -------------------------------------------------------------------------------
> ---- MULTIGRID
> INFO ----
>
> -------------------------------------------------------------------------------
> count for grid 1: 868 cutoff
> [a.u.] 50.00
> count for grid 2: 276 cutoff
> [a.u.] 12.50
> count for grid 3: 80 cutoff
> [a.u.] 3.12
> count for grid 4: 0 cutoff
> [a.u.] 0.78
> total gridlevel count : 1224
>
>
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