negative charge density values

Message

pmignon · #1 Post by **pmignon** » Mon Jul 03, 2006 11:36 am

Hello,
I am performing some calculations on zeolites with alkaline cations and looking to the chgcar file I found negative values. Then I increased the PREC to high, but I still get negative values. I am optimizing the cell, the ions being not moved. here is the INCAR file:

LCHARG=.TRUE.
LWAVE=.FALSE.
LVTOT=.TRUE.

LREAL=Auto
PREC=high
ENCUT=400

IBRION=-1
ISIF=0
EDIFF=1E-5
EDIFFG=0

ISTART=2

IALGO=48
NELMIN=6
NSW=0

NPAR=2

Thanks in advance,
Pierre.

Tyx · #2 Post by **Tyx** » Wed Jul 05, 2006 4:58 pm

Actually, you're not optimising anything...

Unless you mean that you're changing the lattice
parameters manually and then submitting single
point energy calculations...

To optimise the cell and not the ions, you
need ISIF=5, 6, or 7 (read the manual to choose the one
that you need)
You also have to change IBRION and NSW...
<span class='smallblacktext'>[ Edited Wed Jul 05 2006, 07:03PM ]</span>

#3 Post by **admin** » Tue Jul 11, 2006 8:29 am

SMALL (*) negative values in CHGCAR may be due to numerical wiggling of the FFT transforms
(*) please note that the numbers in CHGCAR denote a charge (density * volume of the cell) and have to be divided by V therefore to get charge densities.

pmignon · #4 Post by **pmignon** » Mon Jul 24, 2006 2:10 pm

indeed I noticed that the numbers denote a charge (rho *V). But there is still a problem with getting negative values. So if there is a numerical wiggling of the FFT transform, how can I check that and avoid it ?

Thanks in advance,
Pierre.