CO vibration

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Task

Calculation of the vibrational frequencies of a CO molecule.

Input

POSCAR

CO molecule in a box
 1.0          ! universal scaling parameters
 8.0 0.0 0.0  ! lattice vector  a(1)
 0.0 8.0 0.0  ! lattice vector  a(2)
 0.0 0.0 8.0  ! lattice vector  a(3)
1 1           ! number of atoms for each species
sel           ! selective degrees of freedom are changed
cart          ! positions in cartesian coordinates
 0 0 0       F F T  ! first atom
 0 0 1.143   F F T  ! second atom

Alternatively, try to fix one of the atoms completely.

INCAR

SYSTEM = CO molecule in a box
ISMEAR = 0   ! Gaussian smearing
IBRION = 5   ! use the conjugate gradient algorithm
NFREE = 2    ! central differences
POTIM = 0.02 ! 0.02 A stepwidth 
NSW = 1      ! ionic steps > 0

KPOINTS

Gamma-point only
 0
Monkhorst Pack
 1 1 1
 0 0 0

Calculation

• The selected degrees of freedom are displaced once in the direction $\hat{x}$ and once in $-\hat{x}$ by 0.002 $\AA$ (POTIM).

• In the present case this makes 4 displacements plus the equilibrium positions (i.e. a total of five ionic configurations).

OUTCAR

At the end of the OUTCAR file the following output should be obtained:

SECOND DERIVATIVES (NOT SYMMETRIZED)
------------------------------------
              1Z          2Z
 1Z  -114.737304  114.737304
 2Z   114.458316 -114.458316
  
  
Eigenvectors and eigenvalues of the dynamical matrix
----------------------------------------------------
   
  
  1 f  =   63.887522 THz   401.417139 2PiTHz 2131.058277 cm-1   264.217647 meV
            X         Y         Z           dx          dy          dz
     0.000000  0.000000  0.000000            0           0   -0.655280
     0.000000  0.000000  1.143000            0           0    0.755386

  2 f/i=    0.038494 THz     0.241864 2PiTHz    1.284016 cm-1     0.159198 meV
            X         Y         Z           dx          dy          dz
     0.000000  0.000000  0.000000            0           0   -0.755386
     0.000000  0.000000  1.143000            0           0   -0.655280

Download

COvib.tgz