vasp-分子动力学模拟_vasp smass

文章来源：“分子动力学”公众号

链接：https://mp.weixin.qq.com/s/rpLeA1K5A7eTmeguzFHeAQ

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