Dear Users:
After running extensive test and comparing with other programs using the same ECP and basis sets, it turned out that the ECP implementation in Riper is correct. The reason for the strange results is the parameterization of the default Stuttgart ECP [1]. These ECP were not derived to describe periodic systems, in particular metals and metal surfaces. They were fitted to reproduce calculations on atoms and very small molecules.
Therefore, caution is advised when using the default Stuttgart ECP in Riper for periodic calculations. They may yield unreasonable results, in particular for metals and metal surfaces. We have made few tests and it seems that the large ECP orbital basis for use with the small core potentials due to Christiansen et al [2] give much better results for metallic systems. The ECP and basses can be downloaded as CRENBL (Christiansen-Ross-Ermler-Nash-Bursten) from
https://www.basissetexchange.org/. Please note, that removing exponents lower than 0.1 from basis and auxiliary basis sets will considerably speed up periodic DFT calculations, usually without a significant loss of accuracy.
In addition, in case of SCF convergence problems in Riper try using the following settings:
- It is important to increase the number of DIIS matrices and the accuracy of lattice sums:
$riper
sigma 0.01
epsbext 1.0d-9
mxitdiis 100 - Increase automatic shift and damping:
$scforbitalshift automatic=1.0
$scfdamp start=5.00 step=0.050 min=0.50
[1] D. Andrae, U. Haeussermann, M. Dolg, H. Stoll, H. Preuss, Theor. Chim. Acta 77 (1990) 123. [/li][/list]
[2] (H) - T.H. Dunning, Jr. and P.J. Hay, Methods of Electronic Structure Theory, Vol. 3, H. F. Schaefer III, Ed. Plenum Press (1977); (Li-Ne, Na-Ar) - L. F. Pacios and P. A. Christiansen, J. Chem. Phys. 82 (1985) 2664, doi:10.1063/1.448263; (K-Ca, Sc-Zn, Ga-Kr) - M. M. Hurley et al. J. Chem. Phys. 84 (1986) 6840, doi:10.1063/1.450689; (Rb-Sr,Y-Cd, In) - L. A. LaJohn et al. J. Chem. Phys., 87 (1987) 2812, doi:10.1063/1.453069; (Xe) - M. M. Hurley et al., J. Chem. Phys. 84 (1986) 6840, doi:10.1063/1.450689; (Cs, La, Hf-Hg, Tl-Rn) - R.B. Ross, W.C. Ermler, P.A. Christiansen et al. J. Chem. Phys. 93 (1990) 6654, doi:10.1063/1.458934, erratum: doi:10.1063/1.468517; (Ba, Ce-Lu) - R.B. Ross, W.C. Ermler, S. Das, Unpublished; (Fr-Ra, Ac-Pu) - W.C. Ermler, R.B. Ross, P.A. Christiansen, Int. J. Quant. Chem 40 (1991) 829, doi:10.1002/qua.560400611.
