> Hi dear all Siesta Users, > i tried to reproduce the zone center frequencies in MgO. > But they are not same as shown in JOURNAL OF APPLIED PHYSICS 100, > 023533,2006. In this paper, doubly degenerate freq is ~400 cm-1 and other > is > ~700cm-1 apart from acoustical freqs. > > But Siesta calculates following freqs : > > eigenvalue # 1 omega= -5.342383622781044E-002 > eigenvalue # 2 omega= 9.129011837545617E-003 > eigenvalue # 3 omega= 4.213637115974628E-002 > eigenvalue # 4 omega= 397.442968241599 > eigenvalue # 5 omega= 413.630587428353 > eigenvalue # 6 omega= 413.916231936010 > > I used the basis and pp for MgO as used by J. Junquera et al., Phys. Rev. > B, 64, 235111 (2001), available on siesta site. > > I am wondering, How can i reproduce them? i am attaching the input file. > > I need your help to reproduce the correct frequencies.
Dear Sonu, the mode at 700 cm-1 is LO phonon in MgO; you won't get it without additional effort (calculation of macroscopic polarization etc.). The mode near 400 cm-1 you got not bad, but split as 2+1, instead of being triple degenerate. This is probably because your structure is not exactly cubic (look at your atoms position). I wonder why you use atomic coordinate which looks like the result of relaxation along with lattice parameters which look like given by hand. Relax either both, or none. Good luck Andrei Postnikov
