Add CMake installation for QMCPACK and NEXUS

[prckent]

Based on the request in #1017 , we need to arrange "make install" to work for both QMCPACK and NEXUS. CMake has many options to support this.

I suggest we just focus on the default real cpu build. In later versions we can handle Quantum Espresso, ideally after our converter is in QE, and then complex.

What needs to be installed?

build/bin/*
nexus/executables/*
nexus/library

Although NEXUS is not a python package, there must be some standards to follow.

[jtkrogel]

Happy to do the Nexus part, though not sure what is desired in the "make install" context.

[naromero77]

For reference, this is what I do in the Spack package for install.
https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/qmcpack/package.py#L250

I install all binaries in bin, I copy over the entire Nexus directory, and I "install" the manual.

[naromero77]

For Python, there are usually two options:

1. install in "site-packages" subdirectory of the Python distribution
   OR
2. Add the appropriate directories to PYTHONPATH environment variable.

[jtkrogel]

Thanks Nick. I've generally taken the second option to "install" Nexus.

[prckent]

Regarding NEXUS perhaps copying to $INSTALL_DIR/nexus/... will suffice. It would be good if qmca would work out of the box.

[prckent]

(We'll have to discuss who can handle the QMCPACK side. @PDoakORNL ?)

[jtkrogel]

qmca is fully standalone (no install required). All that is needed is python, numpy, and (optionally) matplotlib.

[markdewing]

I can work on the QMCPACK side, unless @PDoakORNL is already working on it.

[markdewing]

The bin directory contains qmcpack and convert4qmc, which are definitely used and should be installed.
But what about these others? Are they used? Should they be installed?

• getSupercell
• extract-eshdf-kvectors
• checkAffinity

[ye-luo]

We may add or remove files over time. So copy bin/* over.

[markdewing]

Should we adopt some sort of standard for the names of the executables? (add qmc_ prefix, or at least have qmc in the name, as in convert4qmc) In the case where someone installs into a common directory (like /usr/local/bin), so the qmcpack-derived executables can be easily identified.

[prckent]

Good suggestion. At least qmc in the name.

These are mentioned but not described in the manual, so a small update will be needed.

[jtkrogel]

@markdewing are we moving forward with this or are other developments priority at the moment?

[markdewing]

I can get some changes in - rename (#1208) and install should be straightforward.

[prckent]

A prefix for nexus related utilities needs to be chosen carefully. e.g. nx is NoMachine's technology.

[jtkrogel]

I'll have to think more about that.

[jtkrogel]

For the QMCPACK related ones, is this desired?

• qfit -> qmc-fit
• qstat -> qmc-stat
• qtest -> qmc-test
• qmca -> qmca

[jtkrogel]

On the Nexus side, is "nxs-" or "nexus-" better for a prefix? Googling seems to point toward "nxs-" as a better route ("nexus-" prefixed executables are associated with Nexus Wallet), though this is also a file extension.

[prckent]

Should I move the NEXUS part of this to v3.7.0 or is something in the works?

[jtkrogel]

Looking into it. I think installing the Nexus executables this way (a la #1215) should be straightforward.

Less sure if there is a good way to modify the PYTHONPATH environment variable for the user from within CMake to complete the install.

[prckent]

Closed by #1215 and #1242