# [Pw_forum] Warning message - negative or imaginary core charge

Aloysius Soon Sze Lok a.soon at auckland.ac.nz
Thu Jul 1 05:37:49 CEST 2004

```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