Bad RI-MP2 correlation energies

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7:48:15 AM PST - Sun, Dec 11th 2011
I think I may have found an error. I have been running RI-MP2 single point energy calculations on ~30 atom ribonucleosides. I'm using NWCHEM 6.0 on TACC's Lonestar machine (link). Everything seemed ok with the aug-cc-pvdz and aug-cc-pvtz basis sets. But when I tried aug-cc-pvqz, I got really crazy total energies. Here is an example with cytidine: Conformation 1 (aug-cc-pvqz) conf1.nw : SCF energy -886.425706868216 Correlation energy -30.263926310512 Total MP2 energy -916.689633178728 Conformation 2 (aug-cc-pvqz) conf2.nw : SCF energy -886.423257496456 Correlation energy -4.233108269289 Total MP2 energy -890.656365765745 The difference in correlation energy leads to a ~16,000 kcal/mol energy difference between the conformations. Just for comparison, here are the correlation energies at aug-cc-pvtz: Conformation 1: Correlation energy -3.606311785092 Conformation 2: Correlation energy -3.606330351042 Here are some things I've tried, with no success: - Latest development version of NWCHEM - Removing COSMO - Using a direct calculation (vs semidirect) - with or without "freeze atomic" - Using a different computer Thanks for any help you can give, --Niel PS I reported this problem: http://nwchemgit.github.io/Special_AWCforum/st/id62/Odd_correlation_energies_for_R... Might it be related?

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3:51:45 PM PST - Thu, Dec 22nd 2011
Niel, Can you send the output files for the two conformations to be (bert.dejong@pnnl.gov). Bert Quote:Shireham Dec 11th 2:48 pm I think I may have found an error. I have been running RI-MP2 single point energy calculations on ~30 atom ribonucleosides. I'm using NWCHEM 6.0 on TACC's Lonestar machine (link). Everything seemed ok with the aug-cc-pvdz and aug-cc-pvtz basis sets. But when I tried aug-cc-pvqz, I got really crazy total energies. Here is an example with cytidine: Conformation 1 (aug-cc-pvqz) conf1.nw : SCF energy -886.425706868216 Correlation energy -30.263926310512 Total MP2 energy -916.689633178728 Conformation 2 (aug-cc-pvqz) conf2.nw : SCF energy -886.423257496456 Correlation energy -4.233108269289 Total MP2 energy -890.656365765745 The difference in correlation energy leads to a ~16,000 kcal/mol energy difference between the conformations. Just for comparison, here are the correlation energies at aug-cc-pvtz: Conformation 1: Correlation energy -3.606311785092 Conformation 2: Correlation energy -3.606330351042 Here are some things I've tried, with no success: - Latest development version of NWCHEM - Removing COSMO - Using a direct calculation (vs semidirect) - with or without "freeze atomic" - Using a different computer Thanks for any help you can give, --Niel PS I reported this problem: http://nwchemgit.github.io/Special_AWCforum/st/id62/Odd_correlation_energies_for_R... Might it be related?