effect of precision tag on the band gap of a polymer

[shyam]

Dear sir,
I make my incar file for geometry optimisation of a one dimensional polymer like this:
SYSTEM=POLYMER
PREC=Normal
IBRION=2
EDIFF=1.0e-06
EDIFFG=1.0e-05
INIWAV=1
ISTART=0
ICHARG=2
After that I submit the job for band structure by using the CHGCAR CONTCAR file and perform a self-consistent run.

I get the almost correct value of band gap. but the dE value in OSZICAR file was gone only upto 0.392E-02 whereas I had given the value of EDIFFG 1E-05.
To correct this problem, I use the incar file with NSW=200 and ISMEAR=0 AND 1 respectively in two different jobs to see the results.
the value of dE goes to E-05. But the band gap is incorrect in both cases.
I am finding difficulty to understand the reason for this.

Please guide me.

[shyam]

dear sir,
plz help in this case if you can.