The operating system will not allow Spartan to access more memory. The two most common causes for this error are
Spartan cannot run this job with the current memory limits. The most likely cause of this is that you do not have enough RAM in your machine. However, it is also possible that the memory limit is set incorrectly.
This signals that some internal estimation has gone wrong. Essentially the computational engine structured the memory one way, and then realized that it was wrong. Often, an appropriate value for MEM_STATIC=x will be suggested in the verbose output.
The default memory value is also unique for each type machine:
In older versions of Spartan, a parallel job using 2 threads would require twice as much memory. With the newer parallel algorithms included in Spartan'16 Parallel Suite, this is no longer true, and a parallel job uses (essentially) the same amount of memory as a serial job.
Semi-Empirical calculations take much less memory than ab initio calculations, however, requirements can add up for very large systems. As a rough approximation (only good to 1 digit)
where N is the number of atoms.
If using the SM54 Cramer-Truhlar solvation method one can expect another 9*8*(N3)/1024 kB of memory allocated for the Semi-Empirical modification.
In the worst case scenario, you will increase your swap, and Spartan will think your machine has more RAM than it really does. Spartan will then use this "virtual" RAM. Spartan will run, but often the RAM required by Spartan will reside on the disk. Accessing the disk is many order of magnitudes slower than running in RAM, and the speed of Spartan will plummet. A similar problem can occur even if Spartan is using less than the total RAM in your system. If a Spartan job and another program such as a web browser, a java applet, or even another Spartan job are both trying to use the real RAM a thrashing of memory will occur.
There is a case where increasing swap space may help, but be careful as it is easy to create additional issues when changing swap space values. If there are some bloated applications on your machine which are running, but you are not using them, yet you choose not to exit them, they will take up valuable space in memory; Memory which Spartan wants to use. The best thing to do is to quit these applications. But you can also increase swap in the hope that the OS will swap the applications you aren't using out of memory and let Spartan use the real RAM.
When increasing swap it is very important to set the
of Spartan to be less than real Memory in your system.
Typical modern operating systems require a bare minimum of
of RAM to run. So the maximum memory should be:
"MEM_STATIC" refers to an algorithm used partition memory into two different regions for HF and DFT calculations. For discussion purposes let's call them 'STATIC' and 'HEAP' memory. There are times when the algorithm incorrectly predicts the amount of 'STATIC' memory. When this occurs you may get an error message in the verbose output asking for more memory. This can usually be fixed by adding the MEM_STATIC=xx keyword to the output where xx is in megabytes (MB). The default is usually on the order of 32 MB. It is important that this number is significantly less than the total memory allocated in the machine. See the discussion on setting Spartan's memory limits.
Note: This replaces the deprecated keyword MEMORY=yy
where yy was in units of "double-words" (64-bits)
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