How to use this manual

The ORCA manual has been growing for decades and all developers take great care to document and describe all features or ORCA as good as they can. From ORCA 6.0 to ORCA 6.1 this manual has undergone a major restructuring. What you are looking at has been and is a huge team effort and should meet the needs of absolute beginners with little theory background as well as the requirements of experienced developers.

Help us with your feedback

With the initial restructuring of the manual for ORCA 6.1, we made substantial changes that hopefully improve the readbility and general quality of the manual. However, this was only the beginning and we are glad to hear any constructive feedback from you via the ORCA forum on how to improve further future.

The new structure starts with a quickstart guide and a guideline for installation that should get everyone started. The overall structure is ordered such that we first summarize the essential elements of ORCA that a user needs to know when perfoming standard calcuations like how to structure the input, which basis sets and algorithms are available etc. Next, we outline the available electronic structure approaches that can be used to compute energies, structures and properties ranging from Hartree-Fock and DFT to high level ab-initio methods. The next chapter focuses on structure and reactivity and includes all approaches to optimize geometries, find transition states and compute relative (free) energies in various settings. Molecular spectroscopy and properties includes everything that can be computed once a structure has been established and ranges from density and wavefunction analysis to ground- and excited state properties up to complex higher order properties like, for example, MCD. The last few sections deal with important features for complex tasks like running molecular dynamics, multiscalar approaches or orchestrating automated workflows with ORCA using, e.g., the compound script language. Last but not least we have notes on important [utilities] that can be used for post-processing and some technical notes on the ORCA architecture.

Most sections will start with a short outline of the theory with references and some simple examples to get you started, further details like keyword lists and advanced examples are typically found later on in the sections.

We hope that you will find the manual useful and would be very happy if you give feedback online in the ORCA forum.