Dear all, I need to run some calculations for CaCO3 crystals. Because of the nature of the problem (I need the vibrational frequencies of large unit cells) I need an order(N) method, which is available in Siesta.
However, there is a serious problem. The default pseudopotential provided with Siesta has an argon core and leaves only 4s2 electrons in the valence shell. However, as I discussed in an old publication (for GTO-basis set calculations) in Mol. Phys. (Iron, M. A.; Oren, M.; Martin, J. M. L., "Alkali and alkaline earth metal compounds: core-valence basis sets and importance of of subvalence correlation," Molecular Physics 2003, 101, 1345-1361. http://dx.doi.org/10.1080/0026897031000094498 ), when the system has both Ca and O one needs to also include the 3s2 3p6 electrons in the valence shell (i.e., have a neon core). This arises since the occupied 3p orbitals on Ca are higher in energy than the valence 2p of oxygen. Therefore, they need to be included as “honorary” valence electrons. My problem is that I have not been able to figure out how to do this in Siesta. (I have tried a number of codes, which do include the 3s2 3p6 of Ca in the valence shell, but either do not have vibrational frequencies or order(N) methods implemented.) I have tried using Atom to generate a new pseudopotential but it cannot run if there are 2 orbitals of the same angular momentum (i.e., 3s and 4s). I can prepare a pseudopotential adding the 3p6 to the valence shell but not the 3s2, but I am not sure how reasonable this would be. Moreover, I have not been able to get Siesta to accept it – Siesta gives an error message that a PAO.Basis block is needed by I cannot figure out how to prepare such a block. If someone can help me with this problem, it would be greatly appreciated. Thank you in advance for your assistance. Respectfully yours, Mark. ----------------------------------------------------- Dr. Mark Iron, Computational Chemistry Unit, Department of Chemical Research Support, Kimmelman 252, Weizmann Institute of Science, Rehovot, Israel 7610001. Tel: +972 8 934 6218 Fax: +972 8 934 3029 e-mail: [email protected]<mailto:[email protected]> web: http://www.weizmann.ac.il/~coiron/ web: https://www.facebook.com/ChemicalResearchSupport (Department) No trees were killed in the sending of this message. However, a large number of electrons were terribly inconvenienced.
