Ram, First of all, according to your input (LatticeConstant & LatticeVectors), there is only one primitive cell in your calculation. And for FCC, there is only one atom in the primitive cell (please refer to any solid state physics books).
Second, the difference of FCC and BCC lies in the LatticeVectors block if you use the primitive cells (also look at any solid state physics books). Third, if you want more atoms in your system, you need large cell instead of the primitive cell. In you case (14 atoms), you need to tell us more on what you are trying to do so users in this maillist can help you how to construct the cell. Dangxin ________________________________ From: janakiraman balachandran <[email protected]> To: [email protected] Sent: Thu, April 14, 2011 3:34:49 PM Subject: Re: [SIESTA-L] Au unit cell not converging Dear Dangxin Thank you for the reply. Why do you say that i need to give only one atom? How would the program know the difference between FCC and BCC if i give only one atom? I would prefer to do a bulk calculation with 14 atom FCC since i need that output somewhere else. On Thu, Apr 14, 2011 at 5:29 PM, Dangxin Wu <[email protected]> wrote: Are you doing a bulk calculation? There should be only one atom in one unit cell of FCC according to your input cell parameters (at [0, 0, 0]). Looking at the warnings in your output, many of the atoms are repeated (they are exactly the same atom). > >Dangxin > > > > ________________________________ From: janakiraman balachandran <[email protected]> > >To: [email protected] >Cc: Prathibha Ramaprasad <[email protected]> >Sent: Thu, April 14, 2011 3:19:39 PM >Subject: Re: [SIESTA-L] Au unit cell not converging > > >Hi >Thanks for the reply. I use one unit cell of FCC. It has 14 Au atoms. Infact i >visualized them using molden and computed the distance. I dont see anything >wrong with the input > >Ram > > >On Thu, Apr 14, 2011 at 5:07 PM, Prathibha Ramaprasad <[email protected]> wrote: > >Ram, >> >> >>Most likely you have included more atoms than there should be in the unit >>cell, >>for example the ones belonging to an adjacent unit cell (as most crystal >>viewing >>tools do). Carefully examine the atoms at the border of your unit cell and >>remove the extra ones. As siesta uses periodic cells, these atoms overlap and >>give you the error you have mentioned. >> >> >>Prat >> >> >> >>On Thu, Apr 14, 2011 at 1:51 PM, janakiraman balachandran <[email protected]> >>wrote: >> >>Hi >>>I'm trying to run a Au unit cell in siesta. However i'm getting a warning >>>stating the atoms on opposite surfaces are too close (distance 0). >>>Subsequently >>>i get an error that says the leading minor is not positive definite and >>>hence >>>diagonalization cannot be performed. I'm very sure that i have used the >>>correct >>>Lattice distance. I'm not sure what causes the problem. I have attached the >>>fdf >>>file. I have commented the kgrid_Monkhorst_Pack andBandLines. But even with >>>them >>>uncommented, i get the same error >>> >>>I need to make it work as soon as possible. Hence any help to sort this >>>problem >>>would be greatly appreciated >>> >>>Thank you >>> >>>Regards >>>Ram >>> >> >
