13

It's possible to estimate solution-phase dielectric constant from a molecular dynamics simulation using this formula: $$\epsilon_{r} = 1 + \frac{4\pi}{3Vk_{B}T}(\langle \mathbf{P}^{2} \rangle - \langle \mathbf{P} \rangle^{2})$$ Where $V$ is the volume, $k_{B}$ is Boltzmann's constant, $T$ is temperature, and $P$ is the dipole moment defined as: $\mathbf{P} = ...


6

I don't think there is a consensus of norm conserving PP being more accurate. There are some references I am aware of which have calculated dielectric tensor using NC-PP, but without justification though: Yu, E. K.; Stewart, D. A.; Tiwari, S. Ab Initio Study of Polarizability and Induced Charge Densities in Multilayer Graphene Films. Phys. Rev. B - Condens. ...


5

Wait, those are two very different resonances. The one at 150-200 nm is obviously of electronic origin, whereas the one at about 12 microns is related to phonon modes. There is quite a lot of experimental data on SiC properties in the infrared, so if you're looking for the experimental data in the uv range, you might want to specify the range in the search. ...


5

It's not obvious to me that you are doing anything wrong in your calculation. Your result for the crossover energy seems consistent with the literature, e.g. Theodorou et al. (1999) and Petalas et al. (1998) (the former being a computational work, and the latter a synchrotron experiment). What you should note, however, is that you are using a very different ...


3

Aren't you missing the volume in the denominator? And the order of the norm and average is probably off in the second term. The original equation should be $$ \epsilon = 1 + \frac{\langle |\mathbf{M}|^2\rangle - |\langle\mathbf{M}\rangle|^2} {3\epsilon_0 V k_B T} $$ and in units where coulombs constant is one, $k = 1 = (4\pi\epsilon_0)^{-1}$, you get $1/\...


3

Molecules will not be on both sides of the box at once because this is explicitly prevented by most good MD packages. You can calculate distances which take into consideration the PBC. For example, here is a code to calculate all the pairwise distances with periodic boundary conditions (x_size = [16,16,16]) This is modified from periodic boundary conditions ...


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