<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000">Please here is an image of the band structure plot I had for 3x3x1pristine graphene supercell.<br>Is it normal to have this? And why do I see the linearity around the K high symmetry point in papers?<br><br>https://tinyurl.com/3x3image<br><br>And this is the content of input files:<br>SCF<br>====<br><br>&CONTROL<br>calculation = "scf"<br>outdir = "../temp/"<br>prefix = "project"<br>pseudo_dir = "../pseudo"<br>restart_mode = "from_scratch"<br>/<br><br>&SYSTEM<br>a = 7.4017956849<br>c = 18<br>degauss = 1.00000e-02<br>ecutrho = 3.60000e+02<br>ecutwfc = 9.00000e+01<br>ibrav = 4<br>nat = 18<br>ntyp = 1<br>occupations = "smearing"<br>smearing = "marzari-vanderbilt"<br>/<br><br>&ELECTRONS<br>conv_thr = 1.00000e-08<br>mixing_beta = 7.00000e-01<br>diagonalization = "david"<br>electron_maxstep = 200<br>/<br>K_POINTS {automatic}<br>15 15 1 0 0 0<br><br>ATOMIC_SPECIES<br>C 12.01070 C.pbe-n-kjpaw_psl.1.0.0.UPF<br><br><br>ATOMIC_POSITIONS {crystal}<br>C 0.0000000000 0.0000000000 0.2499999997<br>C 0.1111111269 0.2222222537 0.2499999994<br>C -0.0000009773 0.3333325787 0.2499999998<br>C 0.1111119864 0.5555564932 0.2499999999<br>C -0.0000009773 0.6666664440 0.2499999998<br>C 0.1111111269 0.8888888731 0.2499999994<br>C 0.3333335560 0.0000009773 0.2499999998<br>C 0.4444443680 0.2222221840 0.2500000005<br>C 0.3333335560 0.3333325787 0.2499999998<br>C 0.4444435068 0.5555564932 0.2499999999<br>C 0.3333330000 0.6666670000 0.2499999993<br>C 0.4444435068 0.8888880136 0.2499999999<br>C 0.6666674213 0.0000009773 0.2499999998<br>C 0.7777778160 0.2222221840 0.2500000005<br>C 0.6666670000 0.3333330000 0.2500000025<br>C 0.7777778160 0.5555556320 0.2500000005<br>C 0.6666674213 0.6666664440 0.2499999998<br>C 0.7777777463 0.8888888731 0.2499999994<br><br><br><br>Bands<br>======<br><br>&CONTROL<br> calculation = "bands"<br> outdir = "../temp/"<br> prefix = "project"<br> pseudo_dir = "../pseudo"<br>/<br><br>&SYSTEM<br> a = 7.4017956849<br> c = 18<br> degauss = 1.00000e-02<br> ecutrho = 3.60000e+02<br> ecutwfc = 9.00000e+01<br> ibrav = 4<br> nat = 18<br> ntyp = 1<br> nbnd = 144<br> occupations = "smearing"<br> smearing = "marzari-vanderbilt"<br>/<br><br>&ELECTRONS<br> conv_thr = 1.00000e-08<br> mixing_beta = 7.00000e-01<br> diagonalization = "david"<br> electron_maxstep = 200<br>/<br><br><br>K_POINTS {crystal_b}<br>4<br> 0.0000000000 0.0000000000 0.0000000000 50 !G<br> 0.3333333333 0.3333333333 0.0000000000 30 !K<br> 0.5000000000 0.0000000000 0.0000000000 40 !M<br> 0.0000000000 0.0000000000 0.0000000000 0 !G<br><br>ATOMIC_SPECIES<br>C 12.01070 C.pbe-n-kjpaw_psl.1.0.0.UPF<br><br><br>ATOMIC_POSITIONS {crystal}<br>C 0.0000000000 0.0000000000 0.2499999997<br>C 0.1111111269 0.2222222537 0.2499999994<br>C -0.0000009773 0.3333325787 0.2499999998<br>C 0.1111119864 0.5555564932 0.2499999999<br>C -0.0000009773 0.6666664440 0.2499999998<br>C 0.1111111269 0.8888888731 0.2499999994<br>C 0.3333335560 0.0000009773 0.2499999998<br>C 0.4444443680 0.2222221840 0.2500000005<br>C 0.3333335560 0.3333325787 0.2499999998<br>C 0.4444435068 0.5555564932 0.2499999999<br>C 0.3333330000 0.6666670000 0.2499999993<br>C 0.4444435068 0.8888880136 0.2499999999<br>C 0.6666674213 0.0000009773 0.2499999998<br>C 0.7777778160 0.2222221840 0.2500000005<br>C 0.6666670000 0.3333330000 0.2500000025<br>C 0.7777778160 0.5555556320 0.2500000005<br>C 0.6666674213 0.6666664440 0.2499999998<br>C 0.7777777463 0.8888888731 0.2499999994<br><br><hr id="zwchr" data-marker=""><div data-marker=""><b>From: </b>"David Yao ANSI via users" <users@lists.quantum-espresso.org><br><b>To: </b>users@lists.quantum-espresso.org<br><b>Sent: </b>Wednesday, May 31, 2023 5:33:43 PM<br><b>Subject: </b>[QE-users] Linear Dispersion Behavior of Graphene Supercells: Seeking Explanations and Solutions<br></div><br><div data-marker=""><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div>Dear All,<br><br>In studying quantum capacitance of doped graphene, I recently made band structure calculations on pristine graphene using supercells of varying sizes. However, I encountered an unexpected result when increasing the supercell size from 2x2x1 to 4x4x1: the linear dispersion behavior around the K - high symmetry point gradually disappeared. This came as a surprise to me since previous articles I read reported a linear dispersion around the K point for similar supercell sizes. I did some also with a gamma Brillouin zone sampling during scf but had same results.<br><br>What are possible reasons behind this and potential approaches to achieve the desired linear behavior in supercell calculations?<br>Are there specific techniques or considerations that need to be taken into account when working with larger supercells of graphene?<br><br>Thank you in advance for your assistance and expertise. <br><br>Regards,<br>David Ansi<br>Master's student<br>University of Sci. and Tech.(KNUST), Ghana<br><br><br></div></div><br>_______________________________________________<br>The Quantum ESPRESSO community stands by the Ukrainian<br>people and expresses its concerns about the devastating<br>effects that the Russian military offensive has on their<br>country and on the free and peaceful scientific, cultural,<br>and economic cooperation amongst peoples<br>_______________________________________________<br>Quantum ESPRESSO is supported by MaX (www.max-centre.eu)<br>users mailing list users@lists.quantum-espresso.org<br>https://lists.quantum-espresso.org/mailman/listinfo/users<br></div></div></body></html>