Dear users, I would like to perform a phonon calculation at Gamma on a 216-atoms crystalline silicon supercell in which has been added 1 single oxygen (PBE functional). This interstitial O is located 'nearly' in the middle of two Si, and unfortunately, many local minima are possible for its position: C2, C1, C1h, D3d, each of them being separated by a very small energy barrier and a small distance as already shown in Countinho-2000: https://sci-hub.mksa.top/10.1103/physrevb.62.10824
When I calculate phonons of the C1h (that has the smallest energy) within DFPT, I obtain imaginary eigenvalues in the dynamical matrix. Of course, when I look at the corresponding eigenvectors, I see that they are exactly located on the O. Then I manually do a frozen phonon calculation using a displacement equal to the eigenvector and I see a positive curvature of the parabola meaning that the system is well at a minimum. Increasing the size of the displacement in my Frozen phonon permits me to see the double minima switching between C2 and C1h. I suppose that the size of the perturbation in DFPT is too high...? Where can I change it is the code? Best regards, Antoine Jay Inputs in attachment Results: Forces are over converged: Total force = 0.00049 Ry/au Frequencies after DFPT are these freq ( 1- 1) = -118.6 [cm-1] --> ? freq ( 2- 2) = -114.5 [cm-1] --> ? freq ( 3- 3) = -99.2 [cm-1] --> ? freq ( 4- 4) = -38.0 [cm-1] --> ? freq ( 5- 5) = -37.7 [cm-1] --> ? freq ( 6- 6) = -37.7 [cm-1] --> ? freq ( 7- 7) = 87.7 [cm-1] --> A' I+R freq ( 8- 8) = 91.5 [cm-1] --> A' I+R freq ( 9- 9) = 91.8 [cm-1] --> A'' I+R and after simple ASR: # mode [cm-1] [THz] IR 1 -107.94 -3.2359 0.0000 2 -38.83 -1.1640 0.0000 3 -10.69 -0.3206 0.0000 4 -2.67 -0.0801 0.0000 5 8.82 0.2643 0.0000 6 29.09 0.8720 0.0000 7 97.81 2.9324 0.0000 8 98.94 2.9661 0.0000 9 98.97 2.9670 0.0000
O_in_Si.ph.in
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O_in_Si.scf.in
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