# Calculation singlet biradical energy of large structure

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 10:23:36 AM PDT - Tue, Aug 29th 2017 Hi all, Before I begin, I acknowledge that the following are references that I have reviewed in order to get to this point in my work which I will post: http://www.nwchem-sw.org/index.php/Special:AWCforum/st/id305/How_to_get_the_open_shell_sin... I am attempting to perform a broken symmetry calculation on a large structure. To this end, I found u/Edo's advice using the mixang option in the above link. My issue is that there is a discrepancy in the energy I get following this methodology and that of Gaussian's energy prediction. To converge the energy I follow these steps in order: (beneath each step is an example input file) 1) Optimize geometry of structure (restricted calculation) start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITED TO CONSERVE SPACE end basis library 6-31G** end driver xyz outCoord end task dft dft CONVERGENCE density 1e-8 XC B3LYP NOIO NOPRINT DIRECT MAXITER 150 end task dft optimize 2) Use the wavefunction generated by the previous calculation as vector 'input' to perform a BS (unrestricted) calculation start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITTED**** end basis library 6-31G** end dft CONVERGENCE density 1e-8 xc hfexch odft mult 1 DIRECT MAXITER 650 mulliken vectors input input.movecs output symm.mos end task dft set mixang 120. dft xc b3lyp adapt off vectors input symm.mos swap alpha 395 394 output brksymm.mos end task dft dft CONVERGENCE density 1e-8 DIRECT MAXITER 650 xc b3lyp end task dft 3) Use the wavefunction generated by the previous BS an vector 'input' to perform another geometry optimization (unrestricted calculation) start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITED*** end basis library 6-31G** end driver xyz outCoord end task dft dft CONVERGENCE density 1e-8 vectors input brksymm.mos output opt2.mos XC B3LYP NOIO NOPRINT DIRECT MAXITER 150 end task dft optimize 4) Finally, use the wavefunction generated in the previous geometry optimization as vector 'input' to perform a final BS (unrestricted) calculation. start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITED ** end basis library 6-31G** end driver xyz outCoord end task dft dft CONVERGENCE density 1e-8 vectors input brksymm.mos output opt2.mos XC B3LYP NOIO NOPRINT DIRECT MAXITER 150 end task dft optimize Idealistically, I expect the energy of Step 3) and Step 4) (*the second optimization and BS calculation) to be the same, as seen in my Gaussian results. The energy discrepancy I am seeing in these Steps for Nwchem suggest either the wavefunction I am using as input is unstable, or there is an error in my input file. If output files or energy values are necessary, I can provide in another post as I imagine this one is rather lengthy. Any ideas or help would be greatly appreciated

 Zww9 Member Profile Send PM
 Clicked A Few Times Threads 3 Posts 10
 10:30:03 AM PDT - Tue, Aug 29th 2017 Quote:Zww9 Aug 29th 10:23 amHi all, Before I begin, I acknowledge that the following are references that I have reviewed in order to get to this point in my work which I will post: http://www.nwchem-sw.org/index.php/Special:AWCforum/st/id305/How_to_get_the_open_shell_sin... I am attempting to perform a broken symmetry calculation on a large structure. To this end, I found u/Edo's advice using the mixang option in the above link. My issue is that there is a discrepancy in the energy I get following this methodology and that of Gaussian's energy prediction. To converge the energy I follow these steps in order: (beneath each step is an example input file) 1) Optimize geometry of structure (restricted calculation) start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITED TO CONSERVE SPACE end basis library 6-31G** end driver xyz outCoord end task dft dft CONVERGENCE density 1e-8 XC B3LYP NOIO NOPRINT DIRECT MAXITER 150 end task dft optimize 2) Use the wavefunction generated by the previous calculation as vector 'input' to perform a BS (unrestricted) calculation start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITTED**** end basis library 6-31G** end dft CONVERGENCE density 1e-8 xc hfexch odft mult 1 DIRECT MAXITER 650 mulliken vectors input input.movecs output symm.mos end task dft set mixang 120. dft xc b3lyp adapt off vectors input symm.mos swap alpha 395 394 output brksymm.mos end task dft dft CONVERGENCE density 1e-8 DIRECT MAXITER 650 xc b3lyp end task dft 3) Use the wavefunction generated by the previous BS an vector 'input' to perform another geometry optimization (unrestricted calculation) start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITED*** end basis library 6-31G** end driver xyz outCoord end task dft dft CONVERGENCE density 1e-8 vectors input brksymm.mos output opt2.mos XC B3LYP NOIO NOPRINT DIRECT MAXITER 150 end task dft optimize 4) Finally, use the wavefunction generated in the previous geometry optimization as vector 'input' to perform a final BS (unrestricted) calculation. start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITED ** end basis library 6-31G** end driver xyz outCoord end task dft dft CONVERGENCE density 1e-8 vectors input brksymm.mos output opt2.mos XC B3LYP NOIO NOPRINT DIRECT MAXITER 150 end task dft optimize Idealistically, I expect the energy of Step 3) and Step 4) (*the second optimization and BS calculation) to be the same, as seen in my Gaussian results. The energy discrepancy I am seeing in these Steps for Nwchem suggest either the wavefunction I am using as input is unstable, or there is an error in my input file. If output files or energy values are necessary, I can provide in another post as I imagine this one is rather lengthy. Any ideas or help would be greatly appreciated ```I expect the energy of Steps 3) and 4) to be ``` -7475.4358343 -7475.4358343 respectively Edited On 10:05:56 AM PDT - Wed, Aug 30th 2017 by Zww9

 Zww9 Member Profile Send PM
 Clicked A Few Times Threads 3 Posts 10
 10:30:20 AM PDT - Tue, Aug 29th 2017 Quote:Zww9 Aug 29th 10:23 amHi all, Before I begin, I acknowledge that the following are references that I have reviewed in order to get to this point in my work which I will post: http://www.nwchem-sw.org/index.php/Special:AWCforum/st/id305/How_to_get_the_open_shell_sin... I am attempting to perform a broken symmetry calculation on a large structure. To this end, I found u/Edo's advice using the mixang option in the above link. My issue is that there is a discrepancy in the energy I get following this methodology and that of Gaussian's energy prediction. To converge the energy I follow these steps in order: (beneath each step is an example input file) 1) Optimize geometry of structure (restricted calculation) start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITED TO CONSERVE SPACE end basis library 6-31G** end driver xyz outCoord end task dft dft CONVERGENCE density 1e-8 XC B3LYP NOIO NOPRINT DIRECT MAXITER 150 end task dft optimize 2) Use the wavefunction generated by the previous calculation as vector 'input' to perform a BS (unrestricted) calculation start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITTED**** end basis library 6-31G** end dft CONVERGENCE density 1e-8 xc hfexch odft mult 1 DIRECT MAXITER 650 mulliken vectors input input.movecs output symm.mos end task dft set mixang 120. dft xc b3lyp adapt off vectors input symm.mos swap alpha 395 394 output brksymm.mos end task dft dft CONVERGENCE density 1e-8 DIRECT MAXITER 650 xc b3lyp end task dft 3) Use the wavefunction generated by the previous BS an vector 'input' to perform another geometry optimization (unrestricted calculation) start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITED*** end basis library 6-31G** end driver xyz outCoord end task dft dft CONVERGENCE density 1e-8 vectors input brksymm.mos output opt2.mos XC B3LYP NOIO NOPRINT DIRECT MAXITER 150 end task dft optimize 4) Finally, use the wavefunction generated in the previous geometry optimization as vector 'input' to perform a final BS (unrestricted) calculation. start input memory total 56000 mb ```geometry noautoz ``` COORDS OMMITED ** end basis library 6-31G** end driver xyz outCoord end task dft dft CONVERGENCE density 1e-8 vectors input brksymm.mos output opt2.mos XC B3LYP NOIO NOPRINT DIRECT MAXITER 150 end task dft optimize Idealistically, I expect the energy of Step 3) and Step 4) (*the second optimization and BS calculation) to be the same, as seen in my Gaussian results. The energy discrepancy I am seeing in these Steps for Nwchem suggest either the wavefunction I am using as input is unstable, or there is an error in my input file. If output files or energy values are necessary, I can provide in another post as I imagine this one is rather lengthy. Any ideas or help would be greatly appreciated For completeness the following are the coordinates: And I expect the energy of Steps 3) and 4) to be -7475.4358343 -7475.4358343 respectively Edited On 10:06:25 AM PDT - Wed, Aug 30th 2017 by Zww9

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