[Wannier] Negative spread for YBCO

[Blackburn Simon]

Hi,
I am calculating wannier functions for a highly correlated material, but I got negative spreads for some functions :
 WF centre and spread    1  (  1.396087,  1.951657,  4.321091 )   -67.06856766
  WF centre and spread    2  (  1.934788,  1.951531,  5.977162 )     2.40616250
  WF centre and spread    3  (  1.934421,  1.951706,  5.977224 )     2.39819002
  WF centre and spread    4  (  1.934972,  1.951188,  5.976614 )     2.39891922
  WF centre and spread    5  (  1.959096,  1.952858,  6.037811 )     8.83943628
  WF centre and spread    6  (  1.870143,  1.952592,  6.081024 )    19.66047794
  WF centre and spread    7  (  1.972215,  1.937209,  5.988440 )    21.95857517
  WF centre and spread    8  (  1.969876,  1.956152,  6.084227 )    12.08353279
  WF centre and spread    9  (  1.959757,  1.947718,  6.065042 )     9.55748623
  WF centre and spread   10  (  1.935713,  1.964057,  2.114624 )     2.44523435
  WF centre and spread   11  (  2.031171,  2.025423,  1.941027 )     4.06438871
  WF centre and spread   12  (  1.903267,  1.954871,  2.093530 )     1.88270760
  WF centre and spread   13  (  1.917133,  1.936205,  2.150585 )     1.62635224
  WF centre and spread   14  (  0.884877,  1.952352,  7.002234 )  -157.28293063
  WF centre and spread   15  (  1.613742,  1.951188,  8.931454 )   -28.16475747
  WF centre and spread   16  (  1.604912,  1.951940,  8.954071 )   -28.76398600
  WF centre and spread   17  (  1.607723,  1.951161,  8.930750 )   -28.99502259


I changed the functions and also I exclude low energy bands, but I still got negative spreads, however they were not necessarily for the same functions.

I would like to know how come some spreads are negative and how to solve this problem.

Sincerely,
Simon Blackburn 


Here is the input file :

num_iter = 10000
conv_window = 3
num_wann = 70
num_bands = 70
mp_grid = 6 6 6 
begin projections
random
Y:l=0;l=1;l=2
Ba:l=0;l=1
Cu:l=1;l=2
O:l=0;l=1
end projections

begin atoms_frac
Y              5.0000000000E-01  5.0000000000E-01  5.0000000000E-01
Ba              5.0000000000E-01  5.0000000000E-01  1.8342796139E-01
Cu              5.1594053334E-41  3.8011886002E-41  2.2852404443E-23
Cu              6.7359629443E-17  6.6174517631E-17  3.5605414672E-01
O              2.9697060661E-17  2.9174577011E-17  1.5697390332E-01
O              5.0000000000E-01  7.0595436999E-17  3.7983938018E-01
O              1.0290749028E-16  5.0000000000E-01  3.7922374798E-01
O              3.1164471290E-17  5.0000000000E-01  2.2852404443E-23
Ba              5.0000000000E-01  5.0000000000E-01  8.1657203862E-01
Cu              1.2182433813E-16  1.1968098604E-16  6.4394585329E-01
O              1.5948690691E-16  1.5668092666E-16  8.4302609668E-01
O              5.0000000000E-01  1.1526006667E-16  6.2016061983E-01
O              1.4860541987E-16  5.0000000000E-01  6.2077625202E-01
end atoms_frac

begin unit_cell_cart
   3.8338465   0.0000000   0.0000000
   0.0000000   3.9025064   0.0000000
   0.0000000   0.0000000  11.8450852
end unit_cell_cart