P. Löwdin, * Corresponding author: benjamin.debruyne@centraliens.net ? Also at School of Engineering, vol.97, p.1474, 1955.

A. J. Coleman, Rev. Mod. Phys, vol.35, p.668, 1963.

R. Mcweeny, Rev. Mod. Phys, vol.32, p.335, 1960.

E. Davidson, Quantum Chemistry, 1976.

N. N. Lathiotakis and M. A. Marques, The Journal of Chemical Physics, vol.128, p.184103, 2008.

T. L. Gilbert, Phys. Rev. B, vol.12, p.2111, 1975.

M. Deutsch, N. Claiser, S. Pillet, Y. Chumakov, P. Becker et al., Acta Crystallographica Section A, vol.68, p.675, 2012.

M. Deutsch, B. Gillon, N. Claiser, J. Gillet, C. Lecomte et al., IUCrJ, vol.1, p.194, 2014.

N. K. Hansen and P. Coppens, Acta Crystallographica Section A, vol.34, p.909, 1978.

J. Gillet, P. J. Becker, and P. Cortona, Phys. Rev. B, vol.63, p.235115, 2001.

J. Gillet, Acta Crystallographica Section A, vol.63, p.234, 2007.

J. Gillet and P. J. Becker, sagamore XIV: Charge, Spin and Momentum Densities, vol.65, 2004.

J. Gillet, C. Fluteaux, and P. J. Becker, Phys. Rev. B, vol.60, p.2345, 1999.

S. Gueddida, Z. Yan, I. Kibalin, A. B. Voufack, N. Claiser et al., The Journal of chemical physics, vol.148, p.164106, 2018.

S. Pillet, M. Souhassou, Y. Pontillon, A. Caneschi, D. Gatteschi et al., New J. Chem, vol.25, p.131, 2001.

H. Schmider, V. H. Smith, and W. Weyrich, The Journal of Chemical Physics, vol.96, p.8986, 1992.

W. L. Clinton and L. J. Massa, Phys. Rev. Lett, vol.29, p.1363, 1972.

V. G. Tsirelson and R. P. Ozerov, Electron Density and Bonding in Crystals: Principles, Theory and X-ray Diffraction Experiments in Solid State Physics and Chemistry, 1996.

M. J. Cooper, M. Cooper, P. E. Mijnarends, P. Mijnarends, N. Shiotani et al., X-ray Compton scattering, vol.5, 2004.

C. Pisani, Quantum-mechanical ab-initio calculation of the properties of crystalline materials, vol.67, 2012.

L. Vandenberghe and S. Boyd, SIAM Review, vol.38, p.49, 1996.

S. Boyd and L. Vandenberghe, Convex Optimization, 2004.

H. Wolkowicz, R. Saigal, and L. Vandenberghe, Handbook of semidefinite programming: theory, algorithms, and applications, vol.27, 2012.

P. Löwdin, The Journal of Chemical Physics, vol.18, p.365, 1950.

P. Pattison and W. Weyrich, Journal of Physics and Chemistry of Solids, vol.40, p.213, 1979.

W. Weyrich, P. Pattison, and B. Williams, Chemical Physics, vol.41, p.271, 1979.

R. Benesch, S. Singh, and V. Smith, Chemical Physics Letters, vol.10, p.151, 1971.

D. Sivia and J. Skilling, Data analysis: a Bayesian tutorial, 2006.

F. Zhang, The Schur complement and its applications, vol.4, 2006.

D. A. Mazziotti, ESAIM: Mathematical Modelling and Numerical Analysis, vol.41, p.249, 2007.

M. Aps, The MOSEK optimization toolbox for MATLAB manual. Version 8.1, 2017.

J. Löfberg, Proceedings of the CACSD Conference, 2004.

J. , D. Smedt, and W. Keesom, Proceedings of the Koninklijke Akademie Van Wetenschappen Te Amsterdam, vol.27, pp.839-846, 1924.

R. Dovesi, R. Orlando, A. Erba, C. M. Zicovich-wilson, B. Civalleri et al., Int.J. Quantum Chem, vol.114, 2014.

R. Dovesi, V. R. Saunders, C. Roetti, R. Orlando, C. M. Zicovich-wilson et al.,

I. J. Harrison, P. Bush, M. D'arco, M. Llunell, Y. Causà et al., Crystal14 user's manual, 2014.

M. F. Peintinger, D. V. Oliveira, and T. Bredow, Journal of Computational Chemistry, vol.34, p.451, 2013.

B. Civalleri, D. Presti, R. Dovesi, and A. Savin, Chem. Modell, vol.9, p.168, 2012.

, Although density is a non-negative valued function, negative regions appear, as the Fourier series representing density is truncated

, As the 1-RDM is a six-variable function, no convenient graphical reprentation exists apart from restricting the variation of the two position vectors of ?(r, r ) along a path

J. S. Binkley, J. A. Pople, and W. J. Hehre, Journal of the American Chemical Society, vol.102, p.939, 1980.

K. L. Schuchardt, B. T. Didier, T. Elsethagen, L. Sun, V. Gurumoorthi et al., Journal of chemical information and modeling, vol.47, p.1045, 2007.

D. Feller, Journal of computational chemistry, vol.17, p.1571, 1996.