Dear Christoph
I suppose that you can filter out the R0 translation to obtain the  
autocorrelation of the dipole moment across the trajectory.

>      Total    0.2108   -0.3623    0.1151 au,      0.5358   -0.9209    
>  0.2925 Debye

before FFT the autocorrelation function you may also try to convolute  
the autocorrelation function with a truncated exponential decay, an  
old NMR practice that will smooth your power spectrum in the frequency  
domain. I'm sorry but I cannot send you my old executables that have  
been lost in a painful hard-disk failure years ago... :-(

HTH
Giuseppe

Quoting "Christoph Wolf(신소재공학과)" <chw...@postech.ac.kr>:

> Dear all
>
>
> I am currently trying to calculate the IR spectrum by taking the FFT  
> of the Autocorrelation function obtained from a CPMD run in cp.x (QE  
> 6.1).
>
>
> I recently stumbled across a post by Giuseppe Mattioli  
> (http://qe-forge.org/pipermail/pw_forum/2015-July/107471.html)  
> indicating that applying the MP correction would allow to calculate  
> the FFT of the AC of the dipole; hence my attempt. I obtain (for CO2  
> centered inside a large empty box):
>
>
> charge density inside the Wigner-Seitz cell:   16.00000000
>
>
>      reference position (R0):        12.57468453   15.78158723    
> 13.05433235 bohr
>
>
>      Dipole moments (with respect to x0):
>
>      Elect    0.2108   -0.3623    0.1151 au,      0.5358   -0.9209    
>  0.2925 Debye
>
>      Ionic    0.0000    0.0000    0.0000 au,      0.0000    0.0000    
>  0.0000 Debye
>
>      Total    0.2108   -0.3623    0.1151 au,      0.5358   -0.9209    
>  0.2925 Debye
>
>
>      Electrons quadrupole moment       -139.68377611 a.u.
>
>           Ions quadrupole moment        101.51494350 a.u.
>
>          Total quadrupole moment        -38.16883261 a.u.
>
>
>      *********    MAKOV-PAYNE CORRECTION    *********
>
>
>      Makov-Payne correction     0.00000000 a.u. =  0.000 eV (1st order, 1/a0)
>
>                                 0.00001738 a.u. =  0.000 eV (2nd  
> order, 1/a0^3)
>
>                                 0.00001738 a.u. =  0.000 eV (total)
>
>
>      corrected Total energy =   -37.17673195 a.u.
>
>
> Now a LAMMPS script (http://lammps.sandia.gov/threads/msg63251.html)  
> tells me that I am supposed to do the following:
>
>
> calculate the autocorrelation function of the net dipole moment.  
> Compute the Fourier transform of the autocorrelation function to get  
> the spectrum.
>
>
> Now I wonder which quantity to "autocorrelate". Is it
>
>
> "Total_Dipole(timestep)+R0(timestep)"
>
>
> Any help is greatly appreciated, especially I wonder if cppp.x is of  
> any help to me on my journey! Input is below (for the ion dynamics)
>
>
> Best,
>
> Chris
>
>
> Christoph Wolf, Seoul National University, Dept. of Materials  
> Science and Engineering
>
>
>  &control
>     calculation = 'cp'
>     title='CO2  MD'
>     prefix='co2',
>     pseudo_dir = '/home/chris/quantum_espresso/pseudo/',
>     outdir='./'
>     restart_mode='reset_counters',
>     nstep=8000, iprint=10, isave=10,
>     dt=5,
>     ndr=50, ndw=51
>  /
> &SYSTEM
>   ibrav = 1
>   A=15 !relaxed cell value! 5.91 A
>   nat = 3
>   ntyp = 2
>   ecutwfc =80.0
>   assume_isolated='mp'
> /
> &electrons
>         electron_dynamics = 'verlet'
>         emass=700
> /
>  &ions
>         ion_dynamics = 'verlet'
>         ion_temperature='nose'
>         fnosep=70.0
>         tempw=300.0
> /
> ATOMIC_SPECIES
>  C 12.0107 C_ONCV_PBE-Chris.UPF
>  O 15.999 O_ONCV_PBE-Chris.UPF
> ATOMIC_POSITIONS angstrom
>  C   7.19147   7.73724   7.21980
>  O   6.24948   7.68725   5.68537
>  O   6.69993   9.42553   7.92219


-- 
********************************************************
- Article premier - Les hommes naissent et demeurent
libres et égaux en droits. Les distinctions sociales
ne peuvent être fondées que sur l'utilité commune
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est la conservation des droits naturels et
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la propriété, la sûreté et la résistance à l'oppression.
********************************************************

    Giuseppe Mattioli
    CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
    v. Salaria Km 29,300 - C.P. 10
    I 00015 - Monterotondo Stazione (RM)
    Tel + 39 06 90672836 - Fax +39 06 90672316
    E-mail: <giuseppe.matti...@ism.cnr.it>
    http://www.ism.cnr.it/en/staff/giuseppe-mattioli/
    ResearcherID: F-6308-2012


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