我最近写了一个关于超临界水的in文件，里面用到了fix shake命令，但运行的时候一直报错ERROR: Invalid fix style，我对照manuel检查了命令格式，没有发现问题，禁了fix shake后运行又出现ERROR: Invalid compute style，都没查出问题在哪里，请各位大侠不吝赐教，小女子先谢过了
以下是我的in文件
units real
dimension 3
boundary p p p
atom_style full
pair_style lj/charmm/coul/charmm 7.5 8.0 8.0 10.0
bond_style harmonic
angle_style harmonic
read_data data.Mol
angle_coeff 1 55.0000 104.5200
bond_coeff 1 450.0000 0.9572
pair_coeff 1 1 0.1521 3.1507
pair_coeff 1 2 0.0836 1.7753
pair_coeff 2 2 0.0460 0.4000
region 1 block INF INF INF INF INF INF
velocity all create 640 100
velocity all scale 640
#group water type 1 2
fix 1 all shake 0.0001 20 0 b 1 a 1
fix 2 all npt temp 640 760 1000 iso 236.92 236.92 1000 drag 1
timestep 0.01
compute 1 all ke
compute 2 all pe
compute 3 all temp
compute 4 all dilatation/atom
compute 5 all displace/atom
thermo 500
thermo_style custom temp press density vol pe ke etotal enthalpy
run 1000
data文件如下
LAMMPS data file from msi2lmp v3.8 for Mol
6 atoms
4 bonds
2 angles
0 dihedrals
0 impropers
2 atom types
1 bond types
1 angle types
-0.854007846 3.056692154 xlo xhi
-0.764937233 3.145762767 ylo yhi
-1.347689527 2.563010473 zlo zhi
Masses
1 15.999400
2 1.007970
Atoms
1 1 1 -0.798200 0.121798883 0.387575451 0.043193656 0 1 0
2 1 2 0.399100 0.308427222 1.054689176 -0.656528781 0 1 0
3 1 2 0.399100 0.163119246 -0.433256524 -0.481969457 0 1 0
4 2 1 -0.798200 1.973583684 2.001768480 1.988670964 0 -1 0
5 2 2 0.399100 2.453643042 1.441265665 1.343893247 0 -1 0
6 2 2 0.399100 1.587480847 2.690434354 1.408703210 0 -1 0
Bonds
1 1 1 2
2 1 1 3
3 1 4 5
4 1 4 6
Angles
1 1 2 1 3
2 1 5 4 6
fix shake 所需要的rigid panckage 出问题了
在MS里面进行建模，然后再lammps里面运行，建模的有机分子是BMIM-，我们的烷基侧链是丁烷的 文献中提示里面的C-H 采用fix shake 进行constrained，但是一直报错 fix shake
我们的fix shake命令式这样的：
fix mobile0 mobile shake 0.0001 20 10 b 4 6 7 9 11 13 #对bond 4 6 7 9 11 13 进行constrained
结果一直报错，错误如下：
|
fix mobile0 mobile shake 0.0001 20 10 b 4 6 7 9 11 13
ERROR: Shake cluster of more than 4 atoms (../fix_shake.cpp:901)
求大神指点指点的啊 下图是建模基本分子的BMIMPF6
lammps中fix shake只能限制小基团的键长键角，比如水分子，CH3 ，CH2这样比较小的基团，你的碳链太长，应该是这个问题，手册中有详细的介绍， In LAMMPS, only small clusters of atoms can be constrained. This is so the constraint calculation for a cluster can be performed by a single processor, to enable good parallel performance. A cluster is defined as a central atom connected to others in the cluster by constrained bonds. LAMMPS allows for the following kinds of clusters to be constrained: one central atom bonded to 1 or 2 or 3 atoms, or one central atom bonded to 2 others and the angle between the 3 atoms also constrained. This means water molecules or CH2 or CH3 groups may be constrained, but not all the C-C backbone bonds of a long polymer chain，
长碳链lammps貌似是实现不了，如果你懂编程可以自己试试,或者换个软件吧
