Improve existing functionals:
  *) Add XC_FLAGS_STABLE or XC_FLAGS_DEVELOPMENT to all functionals in libxc.

Add functionals:

LDA:
  *) McWeeny c (cited in JCP 69, 1177)
     R. McWeeny, in The New World of Quantum Chemistry, edited by B. Pullman and R. Parr (Reidel, Boston, 1976), p. 3.
  *) Handler x (JCP 61, 4824) 
  *) Rae self-energy correction to x (CPL 18, 574 (1973))
  *) ZLP x (Phys. Rev. A, 47 (1993), p. 918) and k (Chem. Phys. Lett. 232, 31)
  *) Proynov-Kong c [Phys. Rev. A 79, 014103 (2009)] http://journals.aps.org/pra/abstract/10.1103/PhysRevA.79.014103

GGAs:
  *) D.J. Tozer, N.C. Handy, Recent advances in density functional theory, Vol.2
  *) functionals of Della Salla (http://www.theory-nnl.it/software.php)
  *) Liu and Parr (http://pra.aps.org/abstract/PRA/v55/i3/p1792_1)
  *) http://dx.doi.org/10.1063/1.3243845
  *) df-LB94, df-revLB94 http://dx.doi.org/10.1103/PhysRevA.83.012509
  *) Lambda-LB94, Q-LB94, Q-revLB94  http://dx.doi.org/10.1063/1.3684261
  *) BMK (Boese-Martin for kinetics) http://scitation.aip.org/content/aip/journal/jcp/121/8/10.1063/1.1774975
  *) Gilbert and Gill c [CPL 312, 511 (1999)] http://www.sciencedirect.com/science/article/pii/S0009261499008362
  *) BNL (Baer-Neuhauser-Livshits) [Phys. Rev. Lett. 94, 043002 (2005) and Phys. Chem. Chem. Phys. 9, 2932 (2007)] http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.94.043002 and http://pubs.rsc.org/en/content/articlelanding/2007/cp/b617919c
  *) zvPBEint and zvPBEsol http://scitation.aip.org/content/aip/journal/jcp/137/19/10.1063/1.4766324
  *) GAPc and GAPloc http://pubs.acs.org/doi/full/10.1021/ct500073b
  *)  B97GGA-1 and B97-1b (A.J.Cohen,N.C.Handy, Chem.Phys.Lett., 316,160 (2000)) This is a different version of B97-1!!!
  *) B98-1, and VS98-1	(A.J.Cohen,N.C.Handy, Chem.Phys.Lett., 316,160 (2000))

mGGAs:
  *) SCAN (http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.036402 and http://arxiv.org/pdf/1504.03028v1.pdf)
  *) ISM (http://scitation.aip.org/content/aip/journal/jcp/116/15/10.1063/1.1462618)
  *) tau-HTCH
  *) KCIS, B0KCIS, B1KCIS http://jcp.aip.org/resource/1/jcpsa6/v117/i23/p10465_s1
  *) regTPSS http://pubs.acs.org/doi/abs/10.1021/ct300269u
  *) LAP class of functionals [70]
  *) Perdew-Constantin laplacian-level KED functional http://link.aps.org/doi/10.1103/PhysRevB.75.155109
  *) Alternative parametrizations of the TB09 functional http://dx.doi.org/10.1103/PhysRevB.85.155109
  *) MCY1 and MCY2 http://dx.doi.org/10.1063/1.2179072
  *) http://www.sciencedirect.com/science/article/pii/S0009261412007117
  *) spin-polarized Colle-Salvetti -type correlation http://www.sciencedirect.com/science/article/pii/S0009261497002017
  *) B94 [A. D. Becke, Int. J. Quantum Chem. Symp. 28, 625 (1994) and  E. Proynov, Z. Gan, and J. Kong, Chem. Phys. Lett. 455, 103 (2008)]
  *) PK06 [E. Proynov and J. Kong, J. Chem. Theory Comput. 3, 746 (2007)]
  *) tau-HCTH correlation

hybrids:
  *) http://arxiv.org/abs/1205.4999 (versions of HSE)
  *) http://link.aip.org/link/doi/10.1063/1.3524336 (HSE_sol)
  *) doi:10.1021/ct800530u (LR-omegaPBE08)
  *) http://arxiv.org/abs/1211.0387
  *) (CAM-)S12g / (CAM-)S12h http://www.sciencedirect.com/science/article/pii/S0009261413008221
  *) HISS http://scitation.aip.org/content/aip/journal/jcp/127/22/10.1063/1.2822021 [*two* range separation constants!)
  *) hAPBE DOI: 10.1021/ct500902p

hybrid meta:
  *) TPSS1KCIS http://pubs.rsc.org/en/content/articlelanding/2005/cp/b416937a
  *) MPWKCIS1K MPW1KCIS http://pubs.acs.org/doi/pdf/10.1021/jp045141s
  *) PBE1KCIS http://pubs.acs.org/doi/pdf/10.1021/ct049851d
  *) b1b95 (54, 60)
  *) tpsslyp1w (1w class of functionals)
  *) HSEsol [L. Schimka, J. Harl and G. Kresse, JCP 134, 024116 (2011)]
  *) tau-HCTH hybrid 
  
check also "local" hybrids?
V. V. Karasiev, J. Mol. Struct. (THEOCHEM), 493, 21 (1999).
V. V. Karasiev and E. V. Ludeña, Phys. Rev. A 65, 062510 (2002).
V. V. Karasiev and E. V. Ludeña, Phys. Rev. A 65, 032515 (2002).


54: Becke, A. D. Phys. ReV. A 1988, 38, 3098.
60: Becke, A. D. J. Chem. Phys. 1996, 104, 1040.
67: Rey, J.; Savin, A. Int. J. Quantum Chem. 1998, 69, 581.
68: Kreiger, J. B.; Chen, J.; Iafrate, G. J.; Savin, A. In Electronic
  Correlations and Materials Properties; Gonis, A., Kioussis, N., Eds;
  Plenum: New York, 1999; p 463.
69: Toulouse, J.; Savin, A.; Adamo, C. J. Chem. Phys. 2002, 117, 1441.
70: http://dx.doi.org/10.1016/0009-2614(94)01189-3
    http://dx.doi.org/10.1002/qua.560560808
    http://dx.doi.org/10.1002/(SICI)1097-461X(1997)64:4<427::AID-QUA5>3.0.CO;2-Y
    http://link.aip.org/link/doi/10.1063/1.1321309
    http://dx.doi.org/10.1021/ct600372t
