  Organizing a chemical space so that elements with similar properties would
take neighboring places in a sequence can help to predict new materials. In
this paper, we propose a universal method of generating such a one-dimensional
sequence of elements, i.e. at arbitrary pressure, which could be used to create
a well-structured chemical space of materials and facilitate the prediction of
new materials. This work clarifies the physical meaning of Mendeleev numbers,
which was earlier tabulated by Pettifor. We compare our proposed sequence of
elements with alternative sequences formed by different Mendeleev numbers using
the data for hardness, magnetization, enthalpy of formation, and atomization
energy. For an unbiased evaluation of the MNs, we compare clustering rates
obtained with each system of MNs.
