[Pw_forum] Warning message - negative or imaginary core charge

[Aloysius Soon Sze Lok]

Dear all,
I'm running a slab calculation on Cu2O and found this warning message:

     number of k points=   13  gaussian broad. (ryd)=  0.0070     ngauss =   0
                       cart. coord. in units 2pi/a_0
        k(   1) = (   0.0000000   0.0000000   0.0000000), wk =   0.0800000
        k(   2) = (   0.0000000   0.2309401   0.0000000), wk =   0.1600000
        k(   3) = (   0.0000000   0.4618802   0.0000000), wk =   0.1600000
        k(   4) = (   0.2000000   0.3464102   0.0000000), wk =   0.1600000
        k(   5) = (   0.2000000   0.5773503   0.0000000), wk =   0.1600000
        k(   6) = (  -0.2000000   0.1154701   0.0000000), wk =   0.1600000
        k(   7) = (   0.2000000   0.1154701   0.0000000), wk =   0.1600000
        k(   8) = (  -0.4000000   0.2309401   0.0000000), wk =   0.1600000
        k(   9) = (   0.4000000   0.2309401   0.0000000), wk =   0.1600000
        k(  10) = (  -0.2000000   0.3464102   0.0000000), wk =   0.1600000
        k(  11) = (   0.4000000   0.0000000   0.0000000), wk =   0.1600000
        k(  12) = (  -0.4000000   0.4618802   0.0000000), wk =   0.1600000
        k(  13) = (   0.6000000   0.1154701   0.0000000), wk =   0.1600000
 
     G cutoff =  326.7719  (  59669 G-vectors)     FFT grid: ( 40, 40,108)
 
     nbndx  =   428  nbnd   =   107  natomwfc =   140  npwx   =    7475
     nelec  =  178.00 nkb   =   280  ngl    =    2816
  warning: negative or imaginary core charge    -0.000003    0.000000
 
     Initial potential from superposition of free atoms
 
     starting charge = 177.85806
     Starting wfc are random

Is this a serious warning? Or  is the value of -0.000003 small enough to 
ignore? May I know the implications, please? Thank you in advance.



-- 
Aloysius Soon SL
Postgraduate Student
Structural & Computational Chemistry
Chemistry Department
The University Of Auckland, New Zealand
Phone: +64 9 373 7599 ext 88291
Email: a.soon at auckland.ac.nz