[编] 使用vasp进行分子动力学模拟

vasp做分子动力学的好处,由于vasp是近些年开发的比较成熟的软件,在做电子scf速度方面有较好的优势。缺点:可选系综太少。尽管如此,对于大多数有关分子动力学的任务还是可以胜任的。主要使用的系综是 NVT 和 NVE。下面我将对主要参数进行介绍!

一般做分子动力学的时候都需要较多原子,一般都超过100个。当原子数多的时候,k点实际就需要较少了。有的时候用一个k点就行,不过这都需要严格的测试。通常超过200个原子的时候,用一个k点,即Gamma点就可以了。

INCAR
EDIFF 一般来说,用1E-4 或者1E-5都可以,这个参数只是对第一个离子步的自洽影响大一些,对于长时间的分子动力学的模拟,精度小一点也无所谓,但不能太小。
IBRION=0 分子动力学模拟
IALGO=48 一般用48,对于原子数较多,这个优化方式较好。
NSW=1000 多少个时间步长。
POTIM=3 时间步长,单位fs, 通常1到3.
ISIF=2 计算外界的压力.
NBLOCK= 1 多少个时间步长,写一次CONTCAR,CHG和CHGCAR,PCDAT.
KBLOCK=50 NBLOCK*KBLOCK 个步长写一次 XDATCAR.
ISMEAR=-1 费米迪拉克分布.
SIGMA =0.05 单位:电子伏
NELMIN=8 一般用6到8, 最小的电子scf数.太少的话,收敛的不好.
LREAL=A
APACO=10 径向分布函数距离, 单位是埃.
NPACO=200 径向分布函数插的点数.
LCHARG=F 尽量不写电荷密度,否则CHG文件太大.
TEBEG=300 初始温度.
TEEND=300 终态温度。 不设的话,等于TEBEG.
SMASS -3 NVE ensemble;-1 用来做模拟退火。大于0 NVT 系综。

This file determines the kind of job which VASP will perform; single point energy calculation (SPE), geometry optimisation (GO - coarse/fine), molecular dynamics (MD - nve/nvt), spin polarised calculation (mag). Examples can be found in /home/cs/model/vasp_util.

Example: INCAR.spe
$system = single point energy calc
NELMIN = 4 minimum number of electronic SCF cycles
EDIFF = 1E-6 stooping criterion for electronic convergence
NSW = 0 number of ionic shifts
ISMEAR = 0 treatment of partial occupancies of electronic levels

Example: INCAR.coarse
$system = coarse geom optimisation
NELMIN = 4
EDIFF = 1E-2
EDIFFG = -1E-2 stopping criterion for forces Fmax < 0.01 eV/A
IBRION = 2 minimisation method, good away from minimum
ISIF = 3 optimise coords and cell pars
LREAL =.TRUE. do calc in real space - quicker
ISTART = 0 start with a random wavefunction
NSW = 20 maximum of 20 ionic shifts
ISMEAR = 0
LCHARG =.FALSE. don't write CHG and CHGCAR files

Example: INCAR.fine
$system = geom optimisation
NELMIN = 4
EDIFF = 1E-6
EDIFFG = -1E-4
PREC = high increase energy cut-off by 25%
IBRION = 1 minimisation method, good close to minimum
ISIF = 3
NSW = 50
ISMEAR = 0
LCHARG=.FALSE.

Example: INCAR.mag
$system = collinear mag structure calc
IBRION = 1
ISIF = 3
NPAR = 1 forces mag structure to be written in output file
EDIFF = 1E-6
EDIFFG = -1E-3
PREC = high
RWIGS = 1.376 0.900 1.233 1.302 radii for spherical integration of spin density, 1 per atom
ISPIN = 2 do spin polarised calc
MAGMOM = 24*0 5 -5 -5 5 initial mag moments for 28 atoms
NSW = 20

Example: INCAR.nve
$system = molecular dynamics
ALGO = V
MAXMIX = 40
IBRION = 0 do molecular dynamics
NSW = 6000 number of time steps
NBLOCK = 1 store structure every time step
POTIM = 3.0 time step 3fs
TEBEG = 673 target temperature
ISYM = 0 turn off symmetry
SMASS = -3 NVE ensemble
LREAL =.TRUE.
LCHARG =.FALSE.
NELMIN = 4
PREC = LOW reduce energy cut-off by 25% for MD
ISTART = 0
ISMEAR = 0;
SIGMA=0.1

Example: INCAR.nvt
$system = molecular dynamics
ALGO = V
MAXMIX = 40
IBRION = 0
NSW = 6000
NBLOCK = 1
POTIM = 3.0
TEBEG = 673
ISYM = 0
SMASS = 2 NVT ensemble, value determines frequency of coupling to heat bath
LREAL =.TRUE.
LCHARG =.FALSE.
NELMIN = 4
PREC = LOW
ISTART = 0
ISMEAR = 0;
SIGMA=0.1

Example: INCAR.scale
$system = molecular dynamics quench
ALGO = V
MAXMIX = 40
IBRION = 0
NSW = 50
NBLOCK = 5 rescale temperature every 5 steps
POTIM = 3.0
TEBEG = 683 initial temp
TEEND = 673 final temp
ISYM = 0
SMASS = -1 MD with velocity scaling
LREAL =.TRUE.
LCHARG =.FALSE.
NELMIN = 4
PREC = LOW
ISTART = 0
ISMEAR = 0;
SIGMA=0.1

原文链接:http://blog.sciencenet.cn/blog-671981-612445.html

标签: vasp

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