Please give me advice--Charge missing problem.

[tsingyurs]

Hi:

  I am using the 2008.02 version of ATK. Lately, I tried many ways to overcome the charge missing problem in the central region, but failed again and again. Based on the manual, I tried to increase the two parameters, circle_points, integral_lower_bound, by up to 1000 for the circle_points, and 200 to the integral_lower_bound. However, the charges missed again. I tried many other different settings of the two parameters, but got the similar output as follows:


# TwoProbe Calculation
# ----------------------------------------------------------------
# sc  0 : q =  547.89834 e
# sc  1 : q =   64.89974 e  dRho =  2.7342E+00
# sc  2 : q = 1397.30305 e  dRho =  2.6779E+01
# sc  3 : q = 1382.66923 e  dRho =  3.8282E+00
# sc  4 : q =   -1.09351 e  dRho =  2.6675E+01
# sc  5 : q =   -0.41444 e  dRho =  3.4139E+00
# sc  6 : q =   -0.33021 e  dRho =  4.8178E-01
# sc  7 : q =   -0.33087 e  dRho =  1.2603E-02
# sc  8 : q =   -0.46378 e  Etot = 290463.46766 Ry  dRho =  1.4961E+00
# sc  9 : q =   -0.53962 e  Etot = 289847.08189 Ry  dRho =  8.0590E-01  dEtot = -6.1639E+02 Ry
# sc 10 : q =   -0.51623 e  Etot = 290469.08511 Ry  dRho =  8.1110E-01  dEtot =  6.2200E+02 Ry
# sc 11 : q =   -0.51636 e  Etot = 290475.67115 Ry  dRho =  3.9437E-03  dEtot =  6.5860E+00 Ry
# sc 12 : q =   -0.53952 e  Etot = 289846.25750 Ry  dRho =  8.1308E-01  dEtot = -6.2941E+02 Ry
# sc 13 : q =   -0.82279 e  Etot = 289920.05779 Ry  dRho =  1.1340E+00  dEtot =  7.3800E+01 Ry
# sc 14 : q =   -0.82737 e  Etot = 290030.82456 Ry  dRho =  6.9627E-02  dEtot =  1.1077E+02 Ry
# sc 15 : q =   -0.00130 e  Etot = 308399.61965 Ry  dRho =  5.9260E+00  dEtot =  1.8369E+04 Ry
# sc 16 : q =   -0.00130 e  Etot = 308404.60572 Ry  dRho =  1.0974E-03  dEtot =  4.9861E+00 Ry
# sc 17 : q =   -0.00129 e  Etot = 308431.57254 Ry  dRho =  5.8303E-03  dEtot =  2.6967E+01 Ry
# sc 18 : q =   -0.00128 e  Etot = 308464.16944 Ry  dRho =  6.9660E-03  dEtot =  3.2597E+01 Ry
# sc 19 : q =   -0.00122 e  Etot = 308683.14442 Ry  dRho =  4.4389E-02  dEtot =  2.1897E+02 Ry
# sc 20 : q =   -0.00130 e  Etot = 308417.81745 Ry  dRho =  5.4166E-02  dEtot = -2.6533E+02 Ry
# sc 21 : q =   -0.00122 e  Etot = 308673.35470 Ry  dRho =  5.2247E-02  dEtot =  2.5554E+02 Ry
# sc 22 : q =   -0.00123 e  Etot = 308638.51030 Ry  dRho =  6.8094E-03  dEtot = -3.4844E+01 Ry
# sc 23 : q =   -0.00122 e  Etot = 308683.57994 Ry  dRho =  8.7343E-03  dEtot =  4.5070E+01 Ry
# sc 24 : q =   -0.00122 e  Etot = 308688.44967 Ry  dRho =  1.3904E-03  dEtot =  4.8697E+00 Ry
# sc 25 : q =   -0.00122 e  Etot = 308688.49791 Ry  dRho =  1.7615E-05  dEtot =  4.8239E-02 Ry
# sc 26 : q =   -0.00122 e  Etot = 308688.30324 Ry  dRho =  4.4664E-05  dEtot = -1.9467E-01 Ry
# sc 27 : q =   -0.00122 e  Etot = 308688.18942 Ry  dRho =  2.3398E-05  dEtot = -1.1381E-01 Ry
# sc 28 : q =   -0.00122 e  Etot = 308688.12191 Ry  dRho =  1.3595E-05  dEtot = -6.7517E-02 Ry
# sc 29 : q =   -0.00122 e  Etot = 308688.09002 Ry  dRho =  6.5164E-06  dEtot = -3.1891E-02 Ry
# sc 30 : q =   -0.00122 e  Etot = 308688.09932 Ry  dRho =  1.8824E-06  dEtot =  9.2989E-03 Ry
# sc 31 : q =   -0.00122 e  Etot = 308688.09931 Ry  dRho =  5.3135E-10  dEtot = -5.2021E-06 Ry


Does anyone have any idea on this problem ?
Thanks in advance for your kindness.

[Anders Blom]

This is a typical problem, which does not have a universal solution. There are several points to consider:

• Electrode setup
• K-point sampling
• Contour integral parameters
• Temperature

Some of this is quite advanced, but at the same time very fundamental, and perhaps not so well documented. To help users understand these points better I have therefore published a new tutorial on our web site that describes a lot of convergence tricks. Go to quantumwise.com and click on Publications>Tutorials, and you will now find there a PDF document called FeMgO Convergence Tricks.pdf.

Although I have used a spin-polarized system (FeMgO MTJ) as an example, the tips and tricks as such apply generally.