Dear Lihui, >?performing calulation of frequency and zero point > energy of CO2 molecule. However, unfortunately, I have > obtained?negative frequency.
> there are several possible reseaons: Well, you did not include one more reason counting them: there is a physical reason for this as you consider CO2 molecule (the linear chain). Obviously, its physical properties do not change if you rotate it fixing C atom in the cell center. This might lead to negative frequencies. If you like to consider CO2 as a molecule you should use the Gamma point only (i.e. you consider CO2 in a big box). > In addition, I intend to calculate the zero point > energy of system by PHNONS code, but it does not give the > zero point energy and other thermodynamics properties in > output file. How could I do? I need your help > urgently. PH code itself does not calculate these properties. You can try download the QHA code from qe-forge.org. If some troubles with this, please let me know. > I need your help urgently. Please keep in mind our forum consists of volunteers and nobody is oblidged to give you urgent reply. Bests, Eyvaz. P.S. Can you please show eigendisplacements? ------------------------------------------------------------------- Prof. Eyvaz Isaev, Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden Condensed Matter Theory Group, Uppsala University, Sweden Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com