From owner-chemistry ":at:" ccl.net Thu Dec 30 16:44:00 2021 From: "Tian Lu sobereva#sina.com" To: CCL Subject: CCL: Quantum chemistry interoperability library? Message-Id: <-54563-211230140922-722-23YxUK1RSLbJBE9almMgnA : server.ccl.net> X-Original-From: "Tian Lu" Date: Thu, 30 Dec 2021 14:09:20 -0500 Sent to CCL by: "Tian Lu" [sobereva(-)sina.com] It is worth to mention that last year I proposed a new file format (mwfn) for wavefunction storage and exchange. Detailed description of this format as well as example files are available at https://doi.org/10.26434/chemrxiv- 2021-lt04f-v5. A comparison between different wavefunction formats, including wfn, wfx, fch, molden, mkl, NBO.47, is given in the appendix of this document. The purpose of defining mwfn format is to provide an ideal format for recording wavefunction and transferring wavefunction between different quantum chemistry and wavefunction analysis programs. This format has been supported by current version of Multiwfn code. Currently, a very popular format for storing wavefunction is Molden (input file of Molden software), however, there are many limitations or problems, for example (1) Nuclear charge information is not explicitly recorded. This is quite troublesome if pseudopotential is used. (2) Matrics (e.g. Fock matrix, density matrix, various integral matrices) cannot be recorded, however they are needed in many post-process analyses. (3) Cell information cannot be recorded. This makes direct analysis for periodic wavefunction infeasible. (4) The format is loosely defined, leading to severe compatiblity problems (I feel deeply about this point in the process of developing the Multiwfn wavefunction analysis code. Molden files produced by many quantum chemistry codes were found to be non-standard, making the loading unsuccessful or leading to wrong analysis result. I spent a lot of time to make my code compatible with molden files produced by as many programs as possible. Also due to the loose definition of the molden format, the efficiency of loading has been sacrificed to a certain extent for compatibility considerations.) (5) Only basis function of angular momentum up to g is formally supported. However, today's very high-precision calculations sometimes involve h angular momentum. (6) Only a single wavefunction can be recorded. Therefore, wavefunctions produced during scanning or molecular dynamics have to be recorded individually in different files. Some of the above issues are not present in the well-known "fch" file, but the fch file has additional limitations, such as the lack of dedicated fields for recording orbital occupation numbers and orbital irreducible representations. In addition, fch format often contains many irrelevant information. Therefore, in my opinion, fch is also not well-suited as a general-purpose format for recording wavefunctions. The limitations of existing wavefunction formats have been fully considered when defining the mwfn format, hence the various problems mentioned above do not exist. Moreover, the mwfn format is clear, concise and human-readable, and thus it is fairly easy to write and load. I hope that this format could be widely supported by quantum chemistry programs in the future and replace the old Molden format. Finally, it is worth to note that as mentioned in the document introducing the mwfn format, Multiwfn code provides sanity check capability of inputted mwfn file. The mwfn file exported by a new code should be able to pass this check. Therefore, potential problem of improper normalization and incorrect ordering of basis functions in a shell could be easily detected and thus fully avoided. Best regards, Tian Lu Beijing Kein Research Center for Natural Sciences