Dear All,
I am trying to calculate the Bader charges for a molecule which binds via a carboxylate (OCO) group onto a Cu (011) surface.
To do this, I have first obtained the convergence for my system using VASP 5.2.2.
To calculate the Bader charges I have set in my INCAR file the tags:
LAECHG = TRUE
NGXF = 486
NGYF = 140
NGZF = 100
(The default values for NG(X,Y,Z)F were 486/70/50. This for a unit cell of: 35.000 X 5.142 X 3.636 A^3 ).
With these settings, the grids generated by VASP are:
dimension x,y,z ////// NGX = 288 ////// NGY = 42 //////// NGZ = 30
dimension x,y,z ////// NGXF= 486////// NGYF= 140 ////// NGZF= 100
support grid ///////// NGXF= 486 ///// NGYF= 140 ////// NGZF= 100
and the Bader charges obtained by using the last binaries:
Atom type ////// # ////////// X //////// Y /////////// Z //////// CHARGE //////// MIN DIST ////// ATOMIC VOL
--------------------------------------------------------------------------------------------------------------------------------------------------------------
Cu_2 //////////13 ////// 11.6954 ////// 1.2946 ////// 3.6362 ////// 11.0075 ////// 1.1817 ////// 13.3379
Cu_2 //////////14 ////// 11.6864 ////// 3.8668 ////// 3.6349 ////// 10.9996 ////// 1.1842 ////// 13.1022
Cu_1 //////////15 ////// 12.9327 ////// 2.5844 ////// 1.7901 ////// 10.7047 ////// 0.8945 ////// 14.1831
Cu_1 //////////16 ////// 12.9339 ////// 0.0171 ////// 1.8480 ////// 10.7065 ////// 0.8935 ////// 14.1787
C /////////////17 ////// 15.4285 ////// 3.8781 ////// 1.7612 ////// 2.4450 ////// 0.3646 ////// 5.6355
O /////////////23 ////// 14.8625 ////// 4.9736 ////// 2.0816 ////// 7.0849 ////// 0.7555 ////// 17.0275
O /////////////24 ////// 14.8514 ////// 2.7828 ////// 1.4879 ////// 7.0782 ////// 0.7540 ////// 17.1990
The Bader charges look very reasonable to me as they show that the Cu atoms from the first layer (surface layer, Cu_1 atoms in the table) and the C atom give charge to the O atoms. (Oxygen binds directly to Cu_1 atoms). The surface second Cu layer (Cu_2) seems unaffeected (in vacuum I found that Cu=11e, C=4e, O=6e).
As I have read that improved accuracy can be obtain if one consider also the LADDGRID tag, I have added this tag also to my INCAR.
However, this tag seems to have absolutely no impact on the VASP 5.2.2 grid or on Bader charges.
Finally, I have done a last test, considering the ADDGRID tag (no L here !!!). The presence of the ADDGRID tag leads to an increase dimension for the 3-rd grid. Thus, by setting this tag the grids become:
dimension x,y,z ////// NGX = 288 ////// NGY = 42 ////// NGZ = 30
dimension x,y,z ////// NGXF= 486 ////// NGYF= 140 ////// NGZF= 100
support grid ///////// NGXF= 972 ////// NGYF= 280 ////// NGZF= 200
(notice the increased dimension for the 3-rd grid).
The Bader charges modify now, but in a way which surprise me:
Atom type //// # //////// X /////////// Y /////////// Z ////// CHARGE ////// MIN DIST ////// ATOMIC VOL
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Cu_2 ////// 13 ////// 11.6954 ////// 1.2946 ////// 3.6362 ////// 10.8426 ////// 1.0838 ////// 13.1094
Cu_2 ////// 14 ////// 11.6864 ////// 3.8668 ////// 3.6349 ////// 10.7522 ////// 1.0654 ////// 11.9108
Cu_1 ////// 15 ////// 12.9327 ////// 2.5844 ////// 1.7901 ////// 11.4632 ////// 0.9075 ////// 19.4473
Cu_1 ////// 16 ////// 12.9339 ////// 0.0171 ////// 1.8480 ////// 11.2575 ////// 0.8982 ////// 17.6149
C ////////// 17 ////// 15.4285 ////// 3.8781 ////// 1.7612 ////// 2.5873 ////// 0.3576 ////// 6.2301
O ////////// 23 ////// 14.8625 ////// 4.9736 ////// 2.0816 ////// 6.9065 ////// 0.6229 ////// 14.4517
O ////////// 24 ////// 14.8514 ////// 2.7828 ////// 1.4879 ////// 6.8086 ////// 0.6322 ////// 16.1091
Thus, the two Cu atoms from the first layer (Cu_1) no longer give any charge to the oxygens (!!!) but rather receive charge from the Cu atoms from the layer beneath (Cu_2 atoms).
I would like to ask the more experience Bader developers and user to help me clarify:
1) the impact of the ADDGRID tag : is this a useful settings in doing Bader analysis ? Which is your experience in having it in the INCAR ?
2) - and just for curiosity - is the LADDGRID tag of any use ? In my case having it set or not in the INCAR file changes nothing.
Thank you very much for having read my post and for any help or hint !
Ed
PS. I used //// as column delimitator. I am sorry if it does not look good.
ADDGRID tag impact
Moderator: moderators
Re: ADDGRID tag impact
With the ADDGRID tag, it looks like the oxygen atoms still accept charge -- about 0.9 instead of 1.1 e.
You do have to find convergence of the charges with respect to grid density. Using a 2x finer grid is about the minimum for an accurate calculation, and going finer to check for convergence would be good. Perhaps you also don't need such a large vacuum along x! Reducing this will make the charge density files and the calculations less expensive.
You do have to find convergence of the charges with respect to grid density. Using a 2x finer grid is about the minimum for an accurate calculation, and going finer to check for convergence would be good. Perhaps you also don't need such a large vacuum along x! Reducing this will make the charge density files and the calculations less expensive.