105. J. M. Mercero, J. M. Ugalde, M. Piris, “Chemical Reactivity Studies by the Natural-Orbital-Functional 2nd-Order-Møller-Plesset (NOF-MP2) method. Water Dehydrogenation by the Scandium Cation”, Theor. Chem. Acc. , … (2021); arXiv:2012.13202 [physics.chem-ph].

104. J. F. Huan Lew-Yee, M. Piris, J. M. del Campo, “Resolution of the identity approximation applied to PNOF correlation calculations”, J. Chem. Phys. 154, 064102 (2021); arXiv:2012.15662 [physics.chem-ph].

103. R. Quintero-Monsebaiz, L. I. Perea-Ramírez, M. Piris, A. Vela, “Spectroscopic properties of open shell diatomic molecules using Piris Natural Orbital Functionals”, Phys. Chem. Chem. Phys. 23, 2953-2963 (2021).

102. M. Piris, I. Mitxelena, “DoNOF: an open-source implementation of natural-orbital-functional-based methods for quantum chemistry”, Comp. Phys. Comm. 259, 107651 (2021), Code Ocean Capsule; arXiv:2004.06142 [physics.comp-ph].

101. I. Mitxelena, M. Piris, “Analytic gradients for spin multiplets in natural orbital functional theory”, J. Chem. Phys. 153, 044101 (2020); arXiv:2005.02333 [physics.chem-ph].

100. I. Mitxelena, M. Piris, “An efficient method for strongly correlated electrons in two dimensions”, J. Chem. Phys. 152, 064108 (2020); arXiv:1911.10157[cond-mat.str-el].

99. I. Mitxelena, M. Piris, “An efficient method for strongly correlated electrons in one dimension”, J. Phys.: Condens. Matter 32, 17LT01 (2020); arXiv:1912.09312[cond-mat.str-el].

98. M. Piris, “Natural Orbital Functional for Multiplets”, Phys. Rev. A 100, 032508 (2019); arXiv:1908.05501 [physics.chem-ph].

97. X. Lopez, M. Piris, “Performance of the NOF-MP2 method in hydrogen abstraction reactions”, Theor. Chem. Acc. 138, 89 (2019); arXiv:1906.04432 [physics.chem-ph].

96. I. Mitxelena, M. Piris, J. M. Ugalde, “Advances in Approximate Natural Orbital Functional Theory”, in State of The Art of Molecular Electronic Structure Computations: Correlation Methods, Basis Sets and More, edited by Philip Hoggan and Ugo Ancarani, Adv. Quantum Chem. 79, 155-177 (2019). ISBN: 9780128161746. DOI: 10.1016/bs.aiq.2019.04.001

95. R. Quintero-Monsebaiz, I. Mitxelena, M. Rodríguez-Mayorga, A. Vela, M. Piris, “Natural orbital functional for spin-polarized periodic systems”, J. Phys.: Condens. Matter 31, 165501 (2019); arXiv:1901.06942 [physics.chem-ph].

94. M. Piris, “Dynamic electron-correlation energy in the NOF-MP2 method from the orbital-invariant perturbation theory”, Phys. Rev. A 98, 022504 (2018); arXiv:1808.06070 [physics.chem-ph].

93. I. Mitxelena, M. Rodríguez-Mayorga, M. Piris, “Phase Dilemma in Natural Orbital Functional Theory from the N-representability Perspective”, Eur. Phys. J. B 91, 109 (2018); arXiv:1804.06282[physics.chem-ph].

92. I. Mitxelena, M. Piris, “Analytic second-order energy derivatives in natural orbital functional theory”, J. Math. Chem. 56, 1445-1455 (2018); arXiv:1802.05887[physics.chem-ph].

91. M. Piris, “The role of the N-representability in one-particle functional theories” in Many-body approaches at different scales: a tribute to N. H. March on the occasion of his 90th birthday, edited by G. G. N. Angilella and C. Amovilli. Chapter 22, pp. 261-278. New York: Springer (2018). ISBN: 978-3-319-72373-0, 978-3-319-72374-7. DOI: 10.1007/978-3-319-72374-7

90. M. Piris, “The electron pairing approach in Natural Orbital Functional Theory” in Theoretical and Quantum Chemistry at the Dawn of the 21st Century, edited by Ramon Carbó-Dorca and Tanmoy Chakraborty. Series: Innovations in Computational Chemistry. Chapter 22, pp. 593-620. Apple Academic Press (2018). ISBN: 9781771886826. DOI: 10.1201/9781351170963

89. I. Mitxelena, M. Piris, M. A. Rodríguez-Mayorga, “Corrigendum: On the performance of Natural Orbital Functional Approximations in Hubbard model (2017 J. Phys.: Condens. Matter 29 425602)”, J. Phys.: Condens. Matter 30, 089501 (2018).

88. M. Piris, K. Pernal, Comment on “Generalization of the Kohn-Sham system that can represent arbitrary one-electron density matrices”, Phys. Rev. A 96, 046501 (2017); arXiv:1710.07221 [physics.chem-ph].

87. M. Rodríguez-Mayorga, E. Ramos-Cordoba, M. Via-Nadal, M. Piris, E. Matito, “Comprehensive benchmarking of density matrix functional approximations”, Phys. Chem. Chem. Phys. 19, 24029-24041 (2017).

86. I. Mitxelena, M. Piris, M. A. Rodríguez-Mayorga, “On the performance of Natural Orbital Functional Approximations in Hubbard model”, J. Phys.: Condens. Matter 29, 425602 (2017).

85. M. Piris, “Global Method for Electron Correlation”, Phys. Rev. Lett. 119, 063002 (2017); arXiv:1708.03719 [physics.chem-ph].

84. I. Mitxelena, M. Piris, “Analytic gradients for natural orbital functional theory”, J. Chem. Phys. 146, 014102 (2017); arXiv:1612.04673 [physics.chem-ph].

83. L. A. Montero-Cabrera, Y. Pérez-Badell, M. Piris, A. L. Montero-Alejo, J. M. García de la Vega, A. J. C. Varandas, “Similarity measures between excited singlet and triplet electron densities in linear acenes. An application to singlet fission”, Mol. Phys. 114, 3650-3657 (2016) .

82. I. Mitxelena, M. Piris, “Molecular Electric Moments calculated by using Natural Orbital Functional Theory”, J. Chem. Phys. 144, 204108 (2016); arXiv:1608.03167 [physics.chem-ph].

81. M. Piris, N. H. March, “Potential energy curves for P2 and P2+ constructed from a strictly N-representable natural orbital functional”, Physics and Chemistry of Liquids 54, 797 (2016); arXiv:1608.03183 [physics.chem-ph].

80. A. Deveson, D. Cremer, G. Frenking, M. Piris, S. Shaik, “Why Does C2 Cause so Many Problems?”,  ChemistryViews (2016).

79. M. Piris, X. Lopez, J. M. Ugalde, “The Bond Order of C2 from an Strictly N-Representable Natural Orbital Energy Functional Perspective”,  Chemistry -­ A European Journal 22, 4109 (2016).

78. M. Piris, N. H. March, “Chemical and Ionization Potentials: Relation via the Pauli Potential and NOF Theory”, Int. J. Quantum Chem. 116, 805-818 (2016).

77. J. Cioslowski, M. Piris, E. Matito, “Robust validation of approximate 1-matrix functionals with few-electron Harmonium atoms”, J. Chem. Phys. 143, 214101 (2015); arXiv:1511.06564 [physics.chem-ph].

76. X. Lopez, M. Piris, “PNOF5 Calculations Based on the “Thermodynamic Fragment Energy Method”: CnH2n+2 (n=1,10) and (FH)n (n=1,8) as test cases”, Theor. Chem. Acc. 134, 151 (2015).

75. M. Piris, N. H. March, “Low-lying Isomers of Free-space Halogen Clusters with Tetrahedral and Octahedral Symmetry in Relation to Stable Molecules Such as SF6”, J. Phys. Chem. A 119, 10190 (2015) .

74. E. Ramos-Cordoba, X. Lopez, M. Piris, E. Matito, “H4: A Challenging System For Natural Orbital Functional Approximations”, J. Chem. Phys. 143, 164112 (2015); arXiv:1507.08244 [physics.chem-ph].

73. X. Lopez, M. Piris, F. Ruipérez, J. M. Ugalde, “Performance of PNOF6 for Hydrogen Abstraction Reactions”, J. Phys. Chem. A 119, 6981 (2015) .

72. M. Piris, N. H. March, “Is the Hartree-Fock prediction that the chemical potential μ of non-relativistic neutral atoms is equal to minus the ionization potential I sensitive to electron correlation?”, Physics and Chemistry of Liquids 53, 696 (2015) .

71. E. Ramos-Cordoba, P. Salvador, M. Piris, E. Matito, “Two new constraints for the cumulant matrix”, J. Chem. Phys. 141, 234101 (2014) .

70. M. Piris, “Interacting pairs in natural orbital functional theory”, J. Chem. Phys. 141, 044107 (2014) .

69. M. Piris, N. H. March, “Weizsäcker inhomogeneity kinetic energy term for the inhomogeneous electron liquid characterizing some thirty homonuclear diatomic molecules at equilibrium and insight into Teller’s theorem in Thomas-Fermi statistical theory”, Physics and Chemistry of Liquids 52, 804 (2014) .

68. M. Piris, J. M. Ugalde, “Perspective on Natural Orbital Functional Theory”, Int. J. Quantum Chem. 114, 1169 (2014) .

67. M. Piris, F. Ruipérez, J. M. Matxain, “Assessment of the second-order perturbative corrections to PNOF5”, Mol. Phys. 112, 711 (2014) .

66. X. Lopez, M. Piris, M. Nakano, B. Champagne, “Natural Orbital Functional Calculations of Molecular Polarizabilities and Second Hyperpolarizabilities. Hydrogen Molecule as a Test Case”, J. Phys. B:  At. Mol. Opt. Phys. 47, 015101 (2014) .

65. M. Piris, J. M. Matxain, X. Lopez, J. M. Ugalde, “The one-electron picture in the Piris Natural Orbital Functional 5 (PNOF5)”, Book Series: Highlights in Theoretical Chemistry 5, 5-15 (2014), ISBN: 978-3-642-41271-4; 978-3-642-41272-1.

64. M. Piris, J. M. Matxain, X. Lopez, “The intrapair electron correlation in natural orbital functional theory”, J. Chem. Phys. 139, 234109 (2013).

63. E. Jimenez-Izal, J. M. Matxain, M. Piris, J. M. Ugalde, “Second-row Transition-Metal Doping of (ZnS)i, i=12,16, Nanoclusters. Structural and Magnetic Properties”, Computation 1, 31 (2013).

62. M. Piris, “Interpair electron correlation by second-order perturbative corrections to PNOF5”, J. Chem. Phys. 139, 064111 (2013).

61. J. M. Matxain, F. Ruipérez, I. Infante, X. Lopez, J. M. Ugalde, G. Merino, M. Piris, “Communications: Chemical bonding in carbon dimer isovalent series from the natural orbital functional theory perspective”, J. Chem. Phys. 138, 151102 (2013).

60. F. Ruipérez, M. Piris, J. M. Ugalde, J. M. Matxain, “The natural orbital functional theory of the bonding in Cr2, Mo2 and W2”, Phys. Chem. Chem. Phys. 15, 2055 (2013).

59. M. Piris, J. M. Matxain, X. Lopez, J. M. Ugalde, “The one-electron picture in the Piris Natural Orbital Functional 5 (PNOF5)”, Theor. Chem. Acc. 132, 1298 (2013).

58. J. M. Matxain, F. Ruipérez, M. Piris, “Computational Study of Be2 using Piris Natural Orbital Functionals”, J. Mol. Model. 19, 1967 (2013).

57. M. Piris, “Bounds on the PNOF5 natural geminal occupation numbers”, Comput. Theor. Chem. 1003, 123 (2013).

56. M. Piris, “A natural orbital functional based on an explicit approach of the two-electron cumulant”, Int. J. Quantum Chem. 113, 620 (2013).

55. X. Lopez, F. Ruipérez, M. Piris, J. M. Matxain, E. Matito, J. M. Ugalde, “Performance of PNOF5 for radical formation reactions: Hydrogen atom abstraction, C-C and O-O homolytic bond cleavage in selected molecules”, J. Chem. Theory Comput. 8, 2646 (2012).

54. E. Jimenez-Izal, J. M. Matxain, M. Piris, J. M. Ugalde, “Self-assembling endohedrally doped CdS nanoclusters: new porous solid phases of CdS”, Phys. Chem. Chem. Phys. 14, 9676 (2012).

53. M. Piris, J. M. Matxain, X. Lopez, J. M. Ugalde, “The extended Koopmans’ theorem: vertical ionization potentials from Natural Orbital Functional Theory”, J. Chem. Phys. 136, 174116 (2012).

52. J. M. Matxain, M. Piris, J. Uranga, X. Lopez, G. Merino, J. M. Ugalde, “The Nature of the Chemical Bonds from PNOF5 calculations”, ChemPhysChem. 13, 2297 (2012).

51. J. M. Matxain, M. Piris, J. M. Mercero, X. Lopez, J. M. Ugalde, “sp3 hybrid orbitals and ionization energies of methane from PNOF5”, Chem. Phys. Lett. 531, 272 (2012).

50. J. M. Matxain, M. Piris, F. Ruipérez, X. Lopez, J. M. Ugalde, “Front cover article: Homolytic molecular dissociation in natural orbital functional theory”,  Phys. Chem. Chem. Phys. 13, 20129 (2011).

49. M. Piris, X. Lopez, F. Ruipérez, J. M. Matxain, J.M. Ugalde, “A natural orbital functional for multiconfigurational states”, J. Chem. Phys. 134, 164102 (2011).

48. X. Lopez, M. Piris, J. M. Matxain, F. Ruipérez, J. M. Ugalde, “Natural orbital functional theory and reactivity studies of diradical rearrangements: ethylene torsion as a case study”, ChemPhysChem. 12, 1673 (2011) .

47. E. Jimenez-Izal, J. M. Matxain, M. Piris, J. M. Ugalde, “Thermal stability of endohedral first-row transition-metal TM@ZniSi structures, i=12, 16”, Journal of Physical Chemistry C 115, 7829 (2011).

46. X. Lopez, F. Ruipérez, M. Piris, J. M. Matxain, J. M. Ugalde, “Diradicals and diradicaloids in Natural Orbital Functional Theory ”, ChemPhysChem. 12, 1061 (2011) .

45. M. Piris, J. M. Matxain, X. Lopez, J. M. Ugalde, “Communications: The role of the positivity N-representability conditions in Natural Orbital Functional Theory”, J. Chem. Phys. 133, 111101 (2010).

44. J. M. Matxain, M. Piris, X. Lopez, J. M. Ugalde, “Complete Basis Set Calculations by PNOF3”, Chem. Phys. Lett. 499, 164 (2010).

43. X. Lopez, M. Piris, J. M. Matxain, J. M. Ugalde, “Front cover article: Performance of PNOF3 for reactivity studies: X[BO] and X[CN] isomerization reactions (X=H,Li) as a case study”, Phys. Chem. Chem. Phys. 12, 12931, (2010).

42. E. Jimenez-Izal, J.M. Matxain, M. Piris, J.M. Ugalde, “Structure and stability of the endohedrally doped (X@CdS), X= Na, K, Cl, Br, nanoclusters”, Journal of Physical Chemistry C 114, 2476 (2010).

41. M. Piris, J.M Matxain, X. Lopez, J.M. Ugalde, “Communications: Accurate description of atoms and molecules by natural orbital functional theory”, Journal of Chemical Physics 132, 031103 (2010).

40. M. Piris, J.M Matxain, X. Lopez, J.M. Ugalde, “Communications: Spin conserving natural orbital functional theory”, Journal of Chemical Physics 131, 021102 (2009).

39. J. Mercero, M. Piris, J.M. Matxain, X. Lopez, J.M. Ugalde, “Sandwich Complexes of the Metalloaromatic eta3­Al3R3 Ligand”, Journal of American Chemical Society 131, 6949 (2009).

38. J.M. Matxain, M. Piris, X. Lopez, J.M. Ugalde, “Thermally Stable Solids Based on Endohedrally Doped Inorganic Fullerenes”,  Chemistry ­ A European Journal 15, 5138 (2009).

37. M. Piris, J.M. Ugalde, “Iterative diagonalization for orbital optimization in the Natural Orbital Functional Theory”, Journal of Computational Chemistry 30, 2078 (2009).

36. J.M. Matxain, E. Formoso, J.M. Mercero, M. Piris, X. Lopez, J.M. Ugalde, “Magnetic Endohedral Trasition­ Metal­ Doped Semiconducting­ nanoclusters”, Chemistry ­ A European Journal 14, 8547 (2008).

35. M. Piris, J.M. Matxain and J.M. Ugalde, “Piris natural orbital functional study of the dissociation of the radical helium dimer”, Journal of Chemical Physics 129, 014108 (2008).

34. M. Piris, X. Lopez, and J.M. Ugalde, “Electron­pair density relaxation holes”, Journal of Chemical Physics 128, 214105 (2008).

33. M. Piris, X. Lopez, and J.M. Ugalde, “Correlation holes for the helium dimer”, Journal of Chemical Physics 128, 134102 (2008).

32. M. Piris, X. Lopez, and J.M. Ugalde, “Natural orbital functional description of van der Waals interactions. A case study of the effects of the basis set for the helium dimer”, International Journal of Quantum Chemistry 108, 1660 (2008).

31. J.M. Matxain, M. Piris, E. Formoso, J. M. Mercero, X. Lopez, J. M. Ugalde, “Endohedral Stannaspherenes: Mn@Sn12 and its dimer. Ferromagnetic or antiferromagnetic?”, ChemPhysChem 8, 2096 (2007).

30. J.M. Matxain, L.A. Eriksson, J.M. Mercero, X. Lopez, M. Piris, J.M. Ugalde, J. Poater, E. Matito, M. Sola, “New solids based on B12N12 fullerenes”,  Journal of Physical Chemistry C 111, 13354 (2007).

29. M. Piris, X. Lopez, J.M. Ugalde, “Dispersion interactions within the PNOF theory: the helium dimer”, Journal of Chemical Physics 126, 214103 (2007).

28. J.M. Matxain, L.A. Eriksson, E. Formoso, M. Piris, J.M. Ugalde, “Endohedral (X@ZniSi)0,+/­i=4,16 Nanoclusters, X=Li, Na, K, Cl, Br”, Journal of Physical Chemistry C 111, 3560 (2007).

27. M. Piris, “Natural Orbital Functional Theory” in Reduced­-Density­-Matrix Mechanics: With Applications to Many­electron Atoms and Molecules, edited by D. A. Mazziotti, Advances in Chemical Physics, Volume 134, Chapter 14, Wiley, New York, April 2007, ISBN: 978­0­471­ 79056­3.

26. P. Leiva, M. Piris, “Description of high­spin restricted open­shells with the Piris Natural Orbital Functional”, International Journal of Quantum Chemistry 107, 1 (2007).

25. P. Leiva, M. Piris, “Calculation of vertical ionization potentials with the Piris Natural Orbital Functional”, Journal of Molecular Structure: THEOCHEM 770, 45 (2006).

24. M. Piris, “A new approach for the Two­-Electron Cumulant in Natural Orbital Functional theory”, International Journal of Quantum Chemistry 106, 1093 (2006).

23. P. Leiva, M. Piris, “Assessment of a new approach for the two­electron cumulant in natural­ orbital­functional theory”, Journal of Chemical Physics 123, 214102 (2005).

22. P. Leiva, M. Piris, “A Natural Orbital Functional study for the electric response properties of molecules”, Journal of Theoretical and Computational Chemistry 4, 1165 (2005).

21. P. Leiva, M. Piris, “Natural orbital functional theory: Ionization Potentials, Equilibrium Geometries and Vibrational Frequencies”, Journal of Molecular Structure: THEOCHEM 719, 63 (2005).

20. M. Piris, P. Otto, “Natural Orbital Functional for correlation in Polymers”, International Journal of Quantum Chemistry 102, 90 (2005).

19. M. Piris, “Natural orbital functional theory: Molecules and Polymers”, Recent Research Developments in Quantum Chemistry 4, 43-­69, ISBN: 81­7895­139­8, Transworld Research Network, Kerala, India (2004).

18. P. Otto, M. Piris, A. Martinez, J. Ladik, “Dynamic (hyper)polarizability calculations for polymers with linear and cyclic p­conjugated elementary cells”, Synthetic Metals 141,  277 (2004).

17. M. Piris, A. Martinez and P. Otto, “A natural orbital functional approach: Calculation of dielectric properties in molecules”, International Journal of Quantum Chemistry 97, 827 (2004).

16. M. Piris, “Second Cuantization for Fermions”, in Introduction to Advanced Topics in Computational Chemistry, L. Montero, L.A. Díaz and R. Bader (Eds.), ISBN: 959­16­0233­2, 29-39, Havana, Cuba (2003).

15. M. Piris, P. Otto, “A one-­particle density matrix functional for correlation in molecular systems”, International Journal of Quantum Chemistry 94, 317 (2003).

14. M. Sosa­-Albertus, M. Piris, “Conformational analysis of 3,3­-disubstituted benzoylthioureas using X­ray diffraction and ab anitio calculations”, Journal of Molecular Structure 598, 261 (2001).

13. M. Sosa, M. Piris, G. Burton, “3,3-­Dimethylacylthioureas: “S”, “­S”, “U” or “W” Conformation?”, Molecules 5, 445 (2000).

12. M. Piris, P. Otto, “The Improved BCS Method in Polymers”, Journal of Chemical Physics 112, 8187 (2000).

11. M. Sosa, M. Piris, “Estudio estructural de aciltioureas 3­,3­-dimetilsustituidas”, Revista Cubana de Química Vol. 11, No.3, 51 (1999).

10. M. Piris, “Física Cuántica”, ISBN: 959­7136­11­2, Editorial ISCTN, La Habana, Cuba (1999).

9. M. Piris, “A generalized self­consistent­field procedure in the Improved BCS theory”, Journal of Mathematical Chemistry 25, 47 (1999).

8. M. Piris, R. Cruz, “Método de HFB en la correlación molecular”, Revista Cubana de Física 15, 3 (1998).

7. M. Piris, “Analytic Gradients in the Improved BCS Method”, Journal of Mathematical Chemistry 23, 399 (1998).

6. M. Piris, L.A. Montero, N. Cruz, “The BCS approach to electron correlation in the density matrix formalism”, Journal of Chemical Physics 107, 180 (1997).

5. M. Piris, R. Cruz, “A BCS approach to molecular correlation”, International Journal of  Quantum Chemistry 53, 353 (1995).

4. R. Capote, M. Piris, R. Pedrosa, “One and Two Quasiparticle State Densities in the ESM: Combinatorial Approach vs. Exact Results”, Proceedings of the International Conference on Nuclear Data for Science and Technology, Editor J.K. Dickens 1, 490 (1994).

3. R. Capote, E. Herrera, R. Lopez, V. Osorio, M. Piris, “Analysis of experimental data on neutron­induced reactions and development of PCROSS code for the calculation of differential pre­equilibrium spectra”, INDC-247 report, International Atomic Energy Agency (1991).

2. R. Capote, E. Herrera, R. Lopez, V. Osorio, M. Piris, “Analysis of experimental data on neutron­induced reactions and development of PCROSS code for the calculation of differential pre-equilibrium emission spectra with modelling of level density function”, INDC­004 report, International Atomic Energy Agency (1991).

1. V.V. Voronov, M. Piris, V.Y. Ponomarev, “Decay of Giant Resonances”, Soviet Journal of Nuclear Physics 51, 49 (1990).