why the Conduction band rises suddenly at Gamma point

[nulakani]

Dear Vasp users,

I am trying to calculate the band structure for two dimensional carbon based tetragonal cell(P4/NMM).For that I follow,

1. Optimized the cell with 4x4x8 K-Mesh
2. Optimized the monolayer with 9x9x1 with 15ang vacuum along Z-direction
3. SCF run for CHGCAR with 25x25x1
4. NSCF for bands with the KPOINT PATH

KPOINTS
60 ! 60 intersections
Line-mode
rec
0.500 0.500 0.000 M
0.000 0.000 0.000 G

0.000 0.000 0.000 G
0.000 0.500 0.000 X

0.000 0.500 0.000 X
0.500 0.500 0.000 M

and I use MP1 smearing with 0.001 width.

PROBLEM:

when i visualize the vasprun.xml with p4v showing zero bandgap and VB & CB are meeting at G point. But when i run (Graeme Henkelman's group) script to find the bandgap it swows an indirect band gap near the G point.To conform this i plot the homo-lumo of all K-points and i fount that the band energy at G point suddenly rises giving an unexpected results. here I gave #kpoint,E(HOMO),E(LUMO)

35 -3.5571 -2.9741
36 -3.5548 -2.9938
37 -3.5525 -3.0136
38 -3.5502 -3.0338
39 -3.5480 -3.0540
40 -3.5459 -3.0746
41 -3.5438 -3.0954
42 -3.5419 -3.1163
43 -3.5400 -3.1374
44 -3.5382 -3.1589
45 -3.5364 -3.1804
46 -3.5348 -3.2022
47 -3.5333 -3.2241
48 -3.5319 -3.2463
49 -3.5306 -3.2686
50 -3.5293 -3.2912
51 -3.5282 -3.3139
52 -3.5273 -3.3367
53 -3.5264 -3.3598
54 -3.5256 -3.3829
55 -3.5249 -3.4062
56 -3.5243 -3.4297
57 -3.5239 -3.4534
58 -3.5236 -3.4772
59 -3.5234 -3.5011
60 -3.5234 -2.3237----------> G POINT
61 -3.5234 -2.3237----------> G POINT
62 -3.5234 -3.5081
63 -3.5235 -3.4911
64 -3.5238 -3.4742
65 -3.5241 -3.4574
66 -3.5245 -3.4405
67 -3.5250 -3.4238
68 -3.5256 -3.4071
69 -3.5263 -3.3905
70 -3.5271 -3.3740
71 -3.5279 -3.3575
72 -3.5289 -3.3411
73 -3.5299 -3.3248
74 -3.5311 -3.3085
75 -3.5323 -3.2924
76 -3.5337 -3.2763
77 -3.5351 -3.2603
78 -3.5366 -3.2444
79 -3.5383 -3.2286
80 -3.5399 -3.2129
81 -3.5418 -3.1973
82 -3.5436 -3.1817
83 -3.5457 -3.1663
84 -3.5477 -3.1509
85 -3.5499 -3.1356
86 -3.5522 -3.1205
87 -3.5546 -3.1054
88 -3.5571 -3.0905
89 -3.5597 -3.0756
90 -3.5624 -3.0608
91 -3.5651 -3.0462
92 -3.5680 -3.0316
93 -3.5711 -3.0172

The top of the valence band and the Fermi is -3.5234 and the bottom of conduction band is -3.5081 and how they are meeting at fermi level is laso not understandable


and the band gap is calculated with 59 KPOINT(HOMO),62 KPOINT(LUMO) giving an indirect band gap of 0.015 eV.

plz,Can any one tell me,why the CB energy suddenly rises at G POINT & whats the mistake with me????

thanks in advance

[support_vasp]

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