The ElasticConstants analysis object does not allow you computing the elasticity tensor and related elastic constants for 2D materials such graphene, MoS2 and so on. But it is possible to compute the elastic properties of these materials in a manual manner, using the QuantumATK total energy analysis object.
You should do total energy calculations for a set of strained structures and compute the elastic constants and related quantities as described, e.g., in
http://folk.uio.no/ravi/allpapers/106-elastic_SrMnO3.pdf for 3D materials. This approach can be generalized for 2D materials by setting C_13, C_33, C_44, C_55 to zero in the formulas for the energy vs. strain dependence, because there exist only 2 independent elastic constants (C_11, C_12) for a graphene monolayer, and C_66 is just (C_11-C_12)/2. That means that you have to use only 2 independent distortions of the cell, e.g., given by the Eq. (6) and (10) in the paper mentioned.
The elastic constants can be obtained from a polynomial fit of the two data sets for Energy vs. Strain corresponding to the 2 independent distortions.
To conclude, we will consider implementing elastic constants analysis for 2D materials as well. But at the moment there is no option of computing these quantities for 2D materials in an automated manner.
