[Pw_forum] 1D systems

[Michele Pisarra]

Dear QE users,
I used QE to calculate the wave functins of several types of carbon nanotubes. To simulate the 1D nature of this system I used cell parameters such that two of the lattice displacement vectors are much larger than the other one. However this choice lead to a reciprocal space with two very small vectors and so to a very large number of plane waves in the basis set, ecut being fixed. I need to reduce the number of plane waves as much as possible. I tried to make different runs using different lengths for the two "irrelevant" vectors and I found that decreasing this lenght decreases the total energy. However I don't think that the total energy is the good parameter to look at in my case, because the decreasing of the total energy can be due to the interaction between the replica of the system that I want to be zero. So I need a criterion to find the best configuration. Can anyone help me?
Thank you.
Michele Pisarra, PhD Student,
Dipartimento di Fisica, Università della Calabria
Via P. Bucci, Cubo 31 C VI piano, 87036, Rende (CS), Italy
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