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【讨论】pwscf中建立晶体模型
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因为pwscf没有像ms中的visualizer一样的可视化的建立晶体的模块，很多时候很不方便。 这里就来学习如何利用MS的visualizer进行晶体结构的输入。 下面是Input_PW中关于pwscf中的晶体系统的信息。 ------------------------------------------------------------------------------- ibrav is the structure index: ibrav structure celldm(2)-celldm(6) 0 "free", see above not used 1 cubic P (sc) not used 2 cubic F (fcc) not used 3 cubic I (bcc) not used 4 Hexagonal and Trigonal P celldm(3)=c/a 5 Trigonal R celldm(4)=cos(alpha) 6 Tetragonal P (st) celldm(3)=c/a 7 Tetragonal I (bct) celldm(3)=c/a 8 Orthorhombic P celldm(2)=b/a,celldm(3)=c/a 9 Orthorhombic base-centered(bco) celldm(2)=b/a,celldm(3)=c/a 10 Orthorhombic face-centered celldm(2)=b/a,celldm(3)=c/a 11 Orthorhombic body-centered celldm(2)=b/a,celldm(3)=c/a 12 Monoclinic P celldm(2)=b/a,celldm(3)=c/a, celldm(4)=cos(ab) 13 Monoclinic base-centered celldm(2)=b/a,celldm(3)=c/a, celldm(4)=cos(ab) 14 Triclinic celldm(2)= b/a, celldm(3)= c/a, celldm(4)= cos(bc), celldm(5)= cos(ac), celldm(6)= cos(ab) For P lattices: the special axis (c) is the z-axis, one basal-plane vector (a) is along x, the other basal-plane vector (b) is at angle gamma for monoclinic, at 120 degrees for trigonal and hexagonal lattices, at 90 degrees for cubic, tetragonal, orthorhombic lattices sc simple cubic ==================== a1 = a(1,0,0), a2 = a(0,1,0), a3 = a(0,0,1) fcc face centered cubic ==================== a1 = (a/2)(-1,0,1), a2 = (a/2)(0,1,1), a3 = (a/2)(-1,1,0). bcc body entered cubic ==================== a1 = (a/2)(1,1,1), a2 = (a/2)(-1,1,1), a3 = (a/2)(-1,-1,1). simple hexagonal and trigonal(p) ==================== a1 = a(1,0,0), a2 = a(-1/2,sqrt(3)/2,0), a3 = a(0,0,c/a). trigonal(r) =================== for these groups, the z-axis is chosen as the 3-fold axis, but the crystallographic vectors form a three-fold star around the z-axis, and the primitive cell is a simple rhombohedron. The crystallographic vectors are: a1 = a(tx,-ty,tz), a2 = a(0,2ty,tz), a3 = a(-tx,-ty,tz). where c=cos(alpha) is the cosine of the angle alpha between any pair of crystallographic vectors, tc, ty, tz are defined as tx=sqrt((1-c)/2), ty=sqrt((1-c)/6), tz=sqrt((1+2c)/3) simple tetragonal (p) ==================== a1 = a(1,0,0), a2 = a(0,1,0), a3 = a(0,0,c/a) body centered tetragonal (i) ================================ a1 = (a/2)(1,-1,c/a), a2 = (a/2)(1,1,c/a), a3 = (a/2)(-1,-1,c/a). simple orthorhombic (p) ============================= a1 = (a,0,0), a2 = (0,b,0), a3 = (0,0,c) bco base centered orthorhombic ============================= a1 = (a/2,b/2,0), a2 = (-a/2,b/2,0), a3 = (0,0,c) face centered orthorhombic ============================= a1 = (a/2,0,c/2), a2 = (a/2,b/2,0), a3 = (0,b/2,c/2) body centered orthorhombic ============================= a1 = (a/2,b/2,c/2), a2 = (-a/2,b/2,c/2), a3 = (-a/2,-b/2,c/2) monoclinic (p) ============================= a1 = (a,0,0), a2= (b*sin(gamma), b*cos(gamma), 0), a3 = (0, 0, c) where gamma is the angle between axis a and b base centered monoclinic ============================= a1 = ( a/2, 0, -c/2), a2 = (b*cos(gamma), b*sin(gamma), 0), a3 = ( a/2, 0, c/2), where gamma is the angle between axis a and b triclinic ============================= a1 = (a, 0, 0), a2 = (b*cos(gamma), b*sin(gamma), 0) a3 = (c*cos(beta), c*(cos(alpha)-cos(beta)cos(gamma))/sin(gamma), c*sqrt( 1 + 2*cos(alpha)cos(beta)cos(gamma) - cos(alpha)^2-cos(beta)^2-cos(gamma)^2 )/sin(gamma) ) where alpha is the angle between axis b and c beta is the angle between axis a and c gamm is the angle between axis a and b ---------------------------------------------------------------------- 下面以Si为例子 在MS中建立Si的元胞，show symmetry, 我们得到这样一些信息：primitive of face centered-cubic，转换到单胞 a=b=c=5.4307A,转换为原子单位，为：10.25a.u.。三个角为60度,元胞中有2个si原子 坐标分别为： 0 0 0 0.25 0.25 0.25 那么在pwscf中，输入&system部分 ibrav= 2, celldm(1) =10.25, nat= 2, ntyp= 1, 输入&electrons ATOMIC_POSITIONS Si 0.00 0.00 0.00 Si 0.25 0.25 0.25 ======================================================================== 下面以Al为例子， 在MS中建立Al的元胞，show symmetry， 得到：primitive of face centered-cubic，转换到单胞，a=b=c=4.0495A，为7.64a.u.,三个角为60度.元胞中只有1个Al原子 坐标为： 0 0 0 &system ibrav= 2, celldm(1) =7.64, nat= 1, ntyp= 1, &electrons ATOMIC_POSITIONS Al 0.00 0.00 0.00 ========================================================================= 下面以FeSi2为例子， 在MS中建立FeSi2元胞，show symmetry，得到：Tetragonal ，其中元胞内有Si原子，所以为Tetragonal I，ibrav=7， a=b=2.684A，c=5.128A。celldm(1)=5.06,celldm(3)=1.9. Fe 0 0 0 Si 0.5 0.5 0.27 ========================================================================= 下面讨论如何建立Al的单原子线 Al晶体中，Al-Al的键长大约为2.385A，即为1.264a.u.，为了避免线与线直接的相互作用，把celldm(1)=12a.u.,那么celldm(3)=0.375 Al 0 0 0 ========================================================================= |
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2楼2008-03-26 23:47:17
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3楼2008-03-27 14:07:46
