Comparing correlated part of CCSD two-particle density matrix between PySCF and CFOUR #2707
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The density matrix is stored in an order that follows the integral format in ERIs: Line 238 in 0d83af7 Line 295 in 0d83af7 You probably need to compare PySCF OOVV with CFOUR VOVO, PySCF OVOV with CFOUR VVOO This choice of density matrix ordering may not be optimal, it is a result of historical path dependence. The two-PDM was initially structured this way when implementing the FCI code. Subsequently, other post-HF module RDM implementations followed this format. |
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@sunqm Thank you very much for the clarification. I think it also has to do with the notation. I believe, CFOUR uses physicist's notation and PySCF uses chemist's. So, OOVV -> VOVO and OVOV -> VVOO. However, OVVO remains intact,right? I am also concerned that many elements of the blocks are sign-changed between the two codes. Is there any rule for that as well? |
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Hi there,
I am trying to compare the two-particle density matrix calculated by PySCF and CFOUR program. Since CFOUR only gives the correlated part of the 2PDM. I am trying to compare the same from PySCF. I am reading the correlated part of the 2PDM blocks from this function
def _gamma2_outcore(mycc, t1, t2, l1, l2, h5fobj, compress_vvvv=False):and worked with this function,
def _make_rdm2(mycc, d1, d2, with_dm1=True, with_frozen=True, ao_repr=False):Such that I only take the particular blocks without dm1 correction, symmetrizing and multiplying by 2.
Upon comparison, I found that for H2 system with CCSD/STO-3G theoretical level,
I am a bit confused as why they should not match?
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