From my experience (was buying one machine, mostly for DFT, in Dec 2013): right now the widely availvable Intel processors are very fast and efficient, and you can easily build a powerful machine as long as you have money.

My choice: 2 x Intel Xeon E5-2680 v2 (10-core) - that gives you 20 cores in one machine and, due to hyperthreading, in fact 40. Plus 64Gb RAM and standard hard drives / interfaces / graphic card in a quiet (well...) SuperMicro tower. The cost came up to around $7000 before tax in Poland. You could easily replace it by cheaper 8-core processors and get the costs down to around $5000.

Obviously you don't want to run it at home, since the electricity bills will kill you :)

Any multi-core workstation.

Depends on amount of money you have and types of modeling you usually do. For example for DFT and HF you need as much cores as possible; memory and hard drive is usually more or less irrelevant (excluding TD-DFT).

For multi-determinant calculation (TD calculations, CC, MPn, CAS, RAS, CI and so on) you need fast and large hard drive and quite large memory. The amount of memory and disc depends on size of system. However for some methods like MP2, fully direct implementations there is quite economic implementations. For this kind of calculations there is no general recommendation.

From my experience (was buying one machine, mostly for DFT, in Dec 2013): right now the widely availvable Intel processors are very fast and efficient, and you can easily build a powerful machine as long as you have money.

My choice: 2 x Intel Xeon E5-2680 v2 (10-core) - that gives you 20 cores in one machine and, due to hyperthreading, in fact 40. Plus 64Gb RAM and standard hard drives / interfaces / graphic card in a quiet (well...) SuperMicro tower. The cost came up to around $7000 before tax in Poland. You could easily replace it by cheaper 8-core processors and get the costs down to around $5000.

Obviously you don't want to run it at home, since the electricity bills will kill you :)

Thanks to all researchers that gave answers to my question. It seems that money is one of the important factors beside number of cores, kind of calculations and RAM.

mine is i7 with 8GB ram. it is very fast in DFT calculation of molecules less than 30 atoms. But, if you do ions with the same amount of atoms, it will kill you. Ions are really slow. I haven't tried metals yet, hope the info. would help ~

Dear Shubhankar Bhattacharyya

Thanks for your detailed answer. TDP is an important factor in increasing computer speed as I recognized from your answer. I shall try to follow your suggestions.

Dear Rina Dao

i7 with 8Gb ram seems the smallest system that can perform ab intio calculations with reasonable time. Thanks for your answer.