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ORCA The local pair-natural orbital (DLPNO) based coupled cluster method have been managed to investigate large organic molecule and small proteins (linear C150H302 (452 atoms, >8800 basis functions) , Crambin with 644 atoms, and more than 6400 basis functions ,C350H902 (>1000 atoms, > 20000 basis functions)). Riplinger, C., Sandhoefer, B., Hansen, ...


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Note that the DLPNO method is only implemented in ORCA. There are indeed analogous and similarly efficient and accurate methods, the PNO-LCCSD method in Molpro [doi.org/10.1021/acs.jctc.7b00799] and the LNO-CCSD method in MRCC [doi.org/10.1021/acs.jctc.9b00511]. To my knowledge exact analytical gradients are not implemented for either of them. There is an ...


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Multi-reference or single-reference? While it is appreciated that near dissociation there will be a near-degeneracy of orbitals, requiring a multi-reference treatment, fortunately we don't have to worry about this when calculating dissociation energies. For example, the N$_2%$ molecule has profound multi-reference character as you approach the dissociation ...


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I’ll expand on this later but here is the abbreviated version. CTF The CTF code can do very large iterative CCSD and CCSDT using a dense spin-orbital formalism. CCSD up to 55 (50) water molecules with cc-pVDZ http://solomonik.cs.illinois.edu/talks/molssi-monterey-may-2017.pdf The 8-water CCSDT problem in Table 3 took 15 minutes on 1024 nodes of BG/Q and ...


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Supplementing Nike's answer above.. This is actually quite elementary math. Let's say I have an orbital in a basis $|\psi\rangle = \sum_i c_i |i\rangle$ and I want to find the expansion in some other basis set $|J\rangle$. How do I do this? In the new basis set, one has the resolution of the identity $\sum_{JK} |J\rangle \langle J|K\rangle^{-1} \langle K|\...


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What you're describing is very common, and is not limited to GAMESS and Q-Chem. First, here's how to do it in MOLPRO, MRCC, GAMESS, Q-Chem (in fact the only electronic structure software that I regularly use which doesn't allow this type of projection into a bigger basis set, is CFOUR): 1) MOLPRO: basis=cc-pVDZ hf basis=cc-pVQZ hf The HF ...


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As far as I know, analytic gradients for DLPNO-CCSD are not available in ORCA. Analytic first derivatives are available for both closed-shell and high-spin open-shell cases, which could be used for computing other first-order properties. As the first exercise to implement analytic gradients within the DLPNO setup, the DLPNO-MP2 method was considered and the ...


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BDEs are calculated by the below procedure: Calculate initial energy Perform homolytic bond cleavage and separate fragments Calculate energies of the fragments, add the energies together Calculate BDE by comparing the fragment energies to the initial energy The level of theory and basis set is dependent on how accurate you want the results to be. B3LYP ...


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Localized natural orbitals methods allow tackling huge system sizes; some links were already given above. Of course, the accuracy remains sometimes a question in such methods: the methods rely on thresholds, which may not have always been converged! So you should keep in mind that these are not black-box tools like conventional coupled-cluster theory. The ...


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One thing the other answers haven't mentioned is the zero point and thermal corrections to the BDE. As mentioned in the Wikipedia Morse potential article, a geometry optimization will take you, by definition to the equilibrium bond length ($r_e$). If you use this as the low energy state, you're calculating $D_e$. The problem is that a quantum harmonic ...


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I think Nike has answered to all questions adequately enough. I am sharing my understanding as one of the developers of the PNO-based local coupled-cluster (CC) methods, codes for computing response properties in particular. In coupled-cluster theory, the correlated wavefunction is described in terms of "cluster amplitudes" (which are the ...


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I'll answer each of your three questions separately, but the one you say is "most important" will go first 😊 And most importantly, why are they used for correlation calculation? They can significantly reduce the cost of a calculation on a big system, especially when there is a large number of "virtual" orbitals (unoccupied orbitals) in ...


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Note: I have corrected some omissions from my initial answer to avoid any confusion. For a rigorous explanation of the process, I would recommend looking at Susi's answer. The projection process for MOs is actually fairly straightforward. In the following, let $m$ be the dimension of the new basis, $n$ the dimension of the old. Even though getting a guess ...


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I have got your calculation successfully completed: The final electronic energy is -0.928161992153724 a.u. This computation required 318.38 seconds (walltime). My output (and input) files are here. They are the same as yours, except my ZMAT uses my basis set database, which I don't think will make a difference for you,...


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