Yes, the z-component (out-of-plane) of the DOS with nu<20THz should
correspond to the ZA modes.
孙琳 <sunlin18@xxxxxxxxxx> 于 2020年7月8日周三 09:42写道：
Thank you for your kindly reply. I've checked other MD simulations with
PDOS from several references. Indeed, the output depends on the choice of
potentials. Even with AIREBO (or REBO + LJ) via LAMMPS, the peak around
1350 cm-1 is still missing. This is in line with your comments that the
optical phonon cannot be described accurately.
Now, I want to ask for a further question. For my simulations, I want to
consider how the twisted angle influnces the ZA1 and ZA2 modes for tBLG
configuration. Thus, can I use the PDOS (nu <=20 THz) of tBLG with
different twisted angles to discuss qualitatively or quantitatively?
Thank you very much!
*发件人:*"Bruce Fan" <brucenju@xxxxxxxxx>
*发送时间:*2020-07-08 13:36:49 (星期三)
*主题:* [gpumd] Re: questions on PDOS of graphene by GPUMD-2.4-corretion
You need to remember that results of MD simulations depend crucially on
the empirical potential used. The Tersoff potential could not describe the
optical phonons very well and it is not a surprise if some fine details for
the optical phonons are missing or wrong compared to experiments. In this
case, you may need first-principles calculations. What I can say is that
the DOS calculation method implemented in GPUMD has no problem.
On Wed, Jul 8, 2020 at 11:03 AM 孙琳 <sunlin18@xxxxxxxxxx> wrote:
I have tried to use the "compute_dos" command to calculate the PDOS of a
single layer graphene with opt-Tersoff potential and EMD method. The output
is very similiar with that in ex2 of gpumd.
According to references of Balandin, there should be two peaks around
1350 cm-1 (or 40.5 THz) and 1585 cm-1 (or 47.55 THz) for the in-plane
phonons, corresponding to TO mode around BZ edge and LO/TO mode around BZ
origin, respectively. However, the 1350 cm-1 peak is missing in both my
calculations and ex2. Thus, could you help me explain that why the peak in
1350 cm-1 is missing? Is it possible to get the peat around 1350 cm-1 by
just optimizing parameters in ex2? Thank you very much!