24小时热门版块排行榜

返回列表

从心而觅

新虫 (小有名气)

应助: 34 (小学生)
金币: 115.6
红花: 17
帖子: 206
在线: 133小时
虫号: 4330822
注册: 2016-01-04
性别: GG
专业: 理论和计算化学

[交流] 关于vasp计算单个原子的能量的交流已有8人参与

为了计算体系的结合能，按照公式，结合能：E=E(A)+E(B)-E(AB)（注：此处A,B为孤立原子总能，即两个孤立原子结合在一起所释放的能量），我首先计算了“AB”的能量，接着分别计算单个原子“A”“B”的能量，文件如下：
此外POTCAR选用标准的PBE。得到的结果如图。
有如下总结：
1：得到H的能量是-13.51ev，与-13.6ev比较接近,说明计算相对可靠。
2：得到C的能量是-148.49ev，小于Si的-103.87ev，这个我无法理解，按说C要大于Si。
3：为了验证2，我查资料发现有文献报道C的能量在-37ev左右，我重新检查了输入文件，并重算，还跟原来一样，还请大神帮忙解释一下。
4：晶体的总能量我也是通过（energy without entropy）-（atomic energy EATOM）得到，不知这样是否合理？
请各位来交流一下，多谢！

incar.png

kopints.png

poscar.png

能量统计.png

回复此楼

一切有为法，如梦幻泡影！如露亦如电，应作如是观！

1楼 2016-08-15 20:08:30

已阅回复此楼关注TA 给TA发消息送TA红花 TA的回帖

回帖支持 ( 显示支持度最高的前 50 名 )

从心而觅

新虫 (小有名气)

应助: 34 (小学生)
金币: 115.6
红花: 17
帖子: 206
在线: 133小时
虫号: 4330822
注册: 2016-01-04
性别: GG
专业: 理论和计算化学

引用回帖:

15楼: Originally posted by xxxxxxxfc at 2016-08-18 14:07:14
啥叫消除简并，麻烦解释一下。...

摘自vasp手册
大概意思就是为了得到原子的基态能量，将原子放在一个非正方体的晶格内，比如说11Ax10Ax9A的晶格（这样做是为了消除简并）。
9.5 Determining the groundstate energ of atoms
The POTCAR file contains information on the energy of the atom in the reference configuration (i.e. the configuration for
which the PP was generated). Total energies calculated by vasp are with respect to this configuration. The reference calculation,
however, did not allow for spin-polarisation or broken symmetry solutions, which usually lower the energy for gradient
corrected of hybrid functionals. To include these effects properly, it is required to calculate the lowest energy magnetic
groundstate using VASP.
Unfortunately convergence to the symmetry broken spin polarized groundstate can be relatively slow in VASP. The following
INCAR file worked reasonably well for most elements:
ISYM = 0 # no symmetry
ISPIN = 2 # allow for spin polarisation
VOSKOWN = 1 # this is important, in particular for GGA
# but not required for PBE potentials
ISMEAR = 0 # Gaussian smearing, otherwise negative occupancies might come up
SIGMA = 0.002 # tiny smearing width to safely break symmetry
AMIX = 0.2 # mixing set manually
BMIX = 0.0001
NELM = 100 # often many steps are required
ICHARG = 1
Execute VASP twice to three times, consecutively with this input file until energies are converged. Furthermore, we recommend
to use large slightly non-cubic cells, i.e. 12 °A ×13 °A ×14 °A.