Hi, I am a chemical crystallographer attempting to better understand and test usage of "supposedly straightforward" QE vc-relax in optimizing cell constants. I am using form I of paracetamol as a test case. The starting structure is from the 20K neutron data. For this test calculation I am actually following guidelines which were outlined in an article on the subject (J. Chem. Theory Comput. 2014, 10, 3423−3437), the dispersion correction is vdW-DF2.
the experimental lattice parameters are as follows : _cell_length_a 12.667(4) _cell_length_b 9.166(3) _cell_length_c 7.073(3) _cell_angle_alpha 90 _cell_angle_beta 115.51(2) _cell_angle_gamma 90 _cell_volume 741.156 the output form the optimization is _cell_length_a 12.994686 _cell_length_b 9.115636 _cell_length_c 6.461433 _cell_angle_alpha 90.000000 _cell_angle_beta 115.510024 _cell_angle_gamma 90.000000 which is strange because the angle beta is unchanged and the a and c lengths have become inaccurate. I believe the deviation is too high. attached is the .in file I have missed something, and cannot figure out what that is? can anyone help me master the art of predicting reliable cell constants using QE vc-relax? any help is greatly appreciated. -Eric
form1_20K_HXACAN13_relax-vc_all.in
Description: Binary data
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