Dear Prof. Sitangshu Bhattacharya, Thank you for your quick reply and these advice on how to eliminate imaginary frequency.
But it is not reasonable for that pseudo-potential could influence symmetry of modem, and it seems to me that the symmetry of vibration mode is only determined by the symmetry of the crystal. I wonder if the symmetry of the crystal changed when you used a different pseudo-potential to relax the crystal cell? Best regards Zhishuo Huang
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