[Quantum Espresso] H2 molecule

Reference:
https://www.youtube.com/watch?v=OU9i_zeapCU&list=PLGntAYRT8AVmQMyurFoncyOdHljqeGU_R&index=4

---

이 글은 위 레퍼렌스를 정리한 글입니다. 

1. Purpose of the projects

  (1) Calculation of the bond length of H2 molecule 
  (2) Calculation of the dissociation energy of H2 molecule 

2. Bond length and dissociation energy from the reference 

Bond length	(1) 0.74 Å  (2) 1.3984 Bohr
Dissociation Energy	(1) 423 KJ/mol (2) 4.4773 eV/molecule (3) 0.329 Ry/molecule

 

3. Strategy for the problem 

(1) Set the distance between two hydrogen atom by 1 Å 
(2) Relaxing automatically to find optimal bond length by method, "relax"

4. Input file 

&control 
	calculation = 'relax'	
	prefix ='h2'
	pseudo_dir = '/home/cmt323/qe-q.e-6.6/SSSP_precision_pseudos/'
/
&system 
	ibrav=1, celldm(1) = 20; 
	nat = 2, ntyp = 1, 
	ecutwfc = 30.0
/
&electrons
	conv_thr=1.0e-8 
/
&ions                        
	ion_dynamics='bfgs'
/
ATOMIC_SPECIES
 H	1.00784		H_ONCV_PBE-1.0.oncvpsp.upf
ATOMIC_POSITIONS (angstrom)
 H	0.00 0.00 0.00
 H	1.00 0.00 0.00
K_POINTS (automatic)
 1 1 1 0 0 0                 

(1) The first comment
    - ibrav = 1 : for simple cubic 
    - celldm(1) = 20 : large lattice constant 
    → set large length of unit cells to avoid the interaction between the nearest unit cells 
(2) The second comment 
    - the ion name card only exist in the method 'relax' 
(3) The third comment
    - Gamma point calculation 

5. Run program pw.x

$ pw.x < H2O.in > H2O.out

 

6. Results 

(1) From the text files with results 

...
663      Final energy   =      -2.3152440860 Ry
664
665      File ./h2.bfgs deleted, as requested
666 Begin final coordinates
667
668 ATOMIC_POSITIONS (angstrom)
669 H             0.1189048079        0.0000000000        0.0000000000
670 H             0.8810951921        0.0000000000        0.0000000000
671 End final coordinates
...

 

(2) Comparison between the reference and calculation results 

	Reference	Results
Bond Length	- 0.74Å  - 1.3984 Bohr	- 0.763 Å  - Error: 2.998%
Dissociation Energy	- 432 KJ/mol - 4.4773 eV/molecule  - 0.329 Ry/molecule	- Bonding energy: -2.315 Ry  - total energy of two isolated hydrogen atoms : -1.986 Ry - Dissociation energy: 0.3288 Ry - Error: 7.68%

 

 

---

 

7. Error 

1) Error - 1 

(1) Error message 

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
      task #         0
      from  read_namelists  : error #         1
      bad line in namelist &electrons: "&ions" (error could be in the previous line)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

 

(2) Error code 

&control
    calculation = 'relax'
    prefix = 'h2'
    pseudo_dir = '/home/cmt323/q-e-qe-6.6/SSSP_precision_pseudos/'
/
&system
    ibrav = 1, celldm(1) = 20;
    nat = 2, ntyp = 1,
    ecutwfc = 30.0
/
&electrons
    conv_thr=1.0e-8
&ions
    ion_dynamics ='bfgs'
/
ATOMIC_SPECIES
    H   1.00784 H_ONCV_PBE-1.0.oncvpsp.upf
ATOMIC_POSITIONS (angstrom)
    H   0.00    0.00    0.00
    H   1.00    0.00    0.00
K_POINTS (automatic)
    1   1   1   0   0   0

- 문제의 원인: &electrons 네임 태그 뒤에 "/"를 추가하지 않음 

 

1) Error - 2

(1) Error message 

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
      task #         1
      from read_cards : error #         1
      species    H in ATOMIC_POSITIONS is nonexistent
 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

 

(2) Error code 

 

&control
    calculation = 'relax'
    prefix = 'h2'
    pseudo_dir = '/home/cmt323/q-e-qe-6.6/SSSP_precision_pseudos/'
/
&system
    ibrav = 1, celldm(1) = 20;
    nat = 2, ntyp = 1,
    ecutwfc = 30.0
/
&electrons
    conv_thr=1.0e-8
/
&ions
    ion_dynamics ='bfgs'
/
ATOMIC_SPECIES
    H   1.00784 H_ONCV_PBE-1.0.oncvpsp.upf
ATOMIC_POSITIONS (angstrom)
    H   0.00    0.00    0.00
    H   1.00    0.00    0.00
K_POINTS (automatic)
    1   1   1   0   0   0

- 문제의 원인: ATOMIC_SPECIES와 ATOMIC_POSITIONS에서 원소의 부분에 "Tab"을 이용해서 띄우면 안된다.