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!