首先要计算一个氢气分子的孤立能量,再减去两个孤立氢原子能量,将得到氢气分子的结合能。

1. 先计算单个原子能量,POTCAR选取PAW_GGA

INCAR:

PREC=Accurate
ISMEAR=0; SIGMA=0.05
ISPIN=2

KPOINTS:

Monkhorst Pack
0
Monkhorst Pack
1 1 1
0 0 0

POSCAR:

H atom
1
15.0  0.0   0.0
0.0   15.0  0.0
0.0   0.0  15.0
H
1
Cart
0 0 0

得到的能量如下:

Free energy of the ion-electron system (eV) 
--------------------------------------------------- 
alpha Z        PSCENC =         0.00072437 
Ewald energy   TEWEN  =        -1.36188267 
-1/2 Hartree   DENC   =        -6.92165960 
-V(xc)+E(xc)   XCENC  =         2.34398347 
PAW double counting   =         0.74203130       -0.75105109 
entropy T*S    EENTRO =         0.00000000 
eigenvalues    EBANDS =        -7.60619631 
atomic energy  EATOM  =        12.44420649 
--------------------------------------------------- 
free energy    TOTEN  =        -1.10984404 eV

energy without entropy =       -1.10984404  energy(sigma->0) =       -1.10984404

2. 计算H2分子的能量

INCAR:

PREC=Accurate
ISMEAR=0; SIGMA=0.05
ISPIN=2
NSW=5
IBRION=2
POTIM=0.1

KPOINTS

Monkhorst Pack
0
Monkhorst Pack
1 1 1
0 0 0

POSCAR:

H2 molecular
1
8.0  0.0   0.0
0.0   8.0  0.0
0.0   0.0  8.0
H
2
Cart
0 0 0
0 0 0.5

得到的能量如下:

Free energy of the ion-electron system (eV) 
--------------------------------------------------- 
alpha Z        PSCENC =         0.01909948 
Ewald energy   TEWEN  =         9.03591211
-1/2 Hartree   DENC   =       -25.32819184 
-V(xc)+E(xc)   XCENC  =         5.31187543 
PAW double counting   =         8.66129443       -8.70651972 
entropy T*S    EENTRO =         0.00000000 
eigenvalues    EBANDS =       -20.61147888 
atomic energy  EATOM  =        24.88841298 
--------------------------------------------------- 
free energy    TOTEN  =        -6.72959600 eV

energy without entropy =       -6.72959600  energy(sigma->0) =       -6.72959600

得到的CONTCAR文件如下:

H2 molecular                                     
1.00000000000000     
8.0000000000000000    0.0000000000000000    0.0000000000000000 
0.0000000000000000    8.0000000000000000    0.0000000000000000 
0.0000000000000000    0.0000000000000000    8.0000000000000000 
2
Direct 
0.0000000000000000  0.0000000000000000 -0.0155839976608132 
0.0000000000000000  0.0000000000000000  0.0780839976608132 
  
0.00000000E+00  0.00000000E+00  0.00000000E+00 
0.00000000E+00  0.00000000E+00  0.00000000E+00

3. 计算得到结合能

键能计算:
E = − ( TOTEN ( H 2 ) − 2 × TOTEN ( H ) ) = − ( − 6.72959600 − 2 × − 1.10984404 ) = 4.51  eV E = -\left( \text{TOTEN}(\text{H}_2) - 2 \times \text{TOTEN}(\text{H}) \right) = -\left( -6.72959600 - 2 \times -1.10984404 \right) = 4.51 \ \text{eV} E=(TOTEN(H2)2×TOTEN(H))=(6.729596002×1.10984404)=4.51 eV

H-H键长计算:
r = ( x 2 − x 1 ) 2 + ( y 2 − y 1 ) 2 + ( z 2 − z 1 ) 2 = ( 0.0780839976608132 + 0.0155839976608132 ) × 8 = 0.74934   A ˚ r = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2 + (z_2 - z_1)^2} = \left( 0.0780839976608132 + 0.0155839976608132 \right) \times 8 = 0.74934 \ \text{Å} r=(x2x1)2+(y2y1)2+(z2z1)2 =(0.0780839976608132+0.0155839976608132)×8=0.74934 A˚

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