Is Gromacs able to use all the computing power of 2 RTX 3090 TI?

GROMACS version:2021
GROMACS modification:No
The configuration of my system is listed below. Is Gromacs able to use all the computing power of 2 RTX 3090 ti?
board= z690 Maximus
cpu= i9-12900K (16 core)
ram=128 Gig
Graphic= 2* RTX 3090 ti (48 Gig, about 20000 Cuda core)

The absolute performance, and performance/(money spent) figure will depend on the systems you typically want to simulate (mostly, number of atoms in the simulation box: protein + solvent).

It also matters whether you want best throughput (total amount of simulated ns per day) or, less likely, fastest time to solution (faster turnover for a single simulation)

There is also a difference if you are asking how to make best use of this hardware (it is somehow already available to you), or whether this is prospective and you are yet to buy the equipment.

Can you tell a bit more about what you want to achieve regarding the above criteria?

Mainly, I work with engineered proteins. Best throughput (ns/day) It is an important issue for me. I would like to know if GROMACS will be able to pool the power of two GPUs (in my case, two RTX 3090 ti) to achieve maximum performance.

I also wanted to know if Gromacs is compatible with RTX A6000.

My experience with this card is limited, but for my setup the best performance was achieved with two mpi tasks and 8 omp threads (even though the gromacs advices to use maximum of 6). The performance per GPU was reasonable compared to other GPUs considering computing power.

You can use multiple GPUs in a simulation. The efficiency will depend on multiple factors, both hardware and simulation setup. Most importantly: typical simulated system sizes, and typical setup (algrithms/settings used).

Have you tested that your simulation setup is compatible with the GPU-resident multi-GPU mode of mdrun?

Yes. Essentially all NVIDIA GPUs released in the last 8 years or so are supported.

I want to buy the most qualified VGA for my system. Considering that in addition to Gromacs, I also use Alpha Fold and this tool is not compatible with 2 GPU, I wanted to know how Gromacs is capable with two gpu.

As I said, it depends on a number of factors, for small simulation systems you will not see any benefit from a second GPU, for larger ones you may see some but expect a modest benefit when going from 1 to 2 GPUs (compared to e.g. 2 to 4). You might be able to improve scaling if you use an NVLink connector (or if you get a motherboard with 2x16 PCIe 4 lanes), see NVIDIA NVLink 2021 Update and Compatibility Chart | Puget Systems