Pressure study of structural properties and phonons in YBa2Cu3O7

The pressure dependence of crystal structure and vibrational properties of YBa2Cu3O7 is investigated by first-principles calculations based on density functional theory. We have determined the optimized geometry for different unit cell volumes by relaxing the atoms to their force-free positions. The tendency of altered bond strength with pressure is consistent with experim ental investigations and previous c-axis strain calculations. The pressure effect on the three A(1g) phonon frequencies dominated by oxygen vibrations is in very good agreement with experimental investigations showing constan t linear pressure coefficients d omega/dp over a wide range of pressure val ves.