:orphan: .. _mmf_X2C: Molecular mean-field X2C ======================== The molecular-mean-field X2C Hamiltonian (X2Cmmf) is **available** for the following methods: - Coupled Cluster (CC): module RELCCSD - multi-reference (MR) CC: Fock-space CC (including the intermediate Hamiltonian IHFSCC version): module RELCCSD The remaining post-SCF modules are **not supported** yet: - KR-MCSCF - KR-CI - TD-DFT The X2Cmmf Hamiltonian scheme can be used for the Dirac-Coulomb as well as the Dirac-Coulomb-Gaunt Hamiltonian (add .GAUNT to \*\*HAMILTONIAN). One-step X2Cmmf --------------- In order to perform a two-component (MR)CC after a four-component SCF calculation add the keyword .X2Cmmf to the \*\*HAMILTONIAN keyword section: :: **HAMILTONIAN .X2Cmmf After the SCF calculation Dirac will carry out the transformation to two-component prior to the 4-index transformation of the two-electron integrals and the CC run. Two-step X2Cmmf --------------- Besides the one-step X2Cmmf protocol as described above one may also proceed in seperate steps. This may be useful if one would like to use less/more MPI processes in the SCF+decoupling step than in the 4-index/CC calculation. The first step (SCF+decoupling) simply requires the .X2Cmmf keyword under the \*\*HAMILTONIAN input deck (same as above): :: **HAMILTONIAN .X2Cmmf Save the files DFCOEF, AOMOMAT and X2CMAT, for example using the *pam* script:: ./pam ... --outcmo --get="AOMOMAT X2CMAT" To restart now any further calculation, for example the 4-index transformation (MOLTRA) and/or the (MR)CC run copy the above files to your scratch directory:: ./pam ... --incmo --put="AOMOMAT X2CMAT" and set the keyword combination as indicated below under the \*\*HAMILTONIAN input deck:: **HAMILTONIAN .X2C *X2C .mmf-restart In order to run a (MR)CC calculation add also the following keyword(s) to the namelist RELCCSSD input:: *CCSORT .USEOE .NORECMP END or the new RELCCSD deck input:: *CCSORT .NORECMP Dirac will automatically read the two-component coefficients from the file DFCOEF and proceed in two-component mode for any wave function analysis or post-HF step required for a (MR)CC calculation.