using System;
using System.Security.Cryptography;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string source = "Hello World!";
            using (SHA512 sha512Hash = SHA512.Create())
            {
                //From String to byte array
                byte[] sourceBytes = Encoding.UTF8.GetBytes(source);
                byte[] hashBytes = sha512Hash.ComputeHash(sourceBytes);
                string hash = BitConverter.ToString(hashBytes).Replace("-", String.Empty);

                Console.WriteLine("The SHA512 hash of " + source + " is: " + hash);
            }
        }
    }
}

Output: The SHA512 hash of Hello World! is: 861844D6704E8573FEC34D967E20BCFEF3D424CF48BE04E6DC08F2BD58C729743371015EAD891CC3CF1C9D34B49264B510751B1FF9E537937BC46B5D6FF4ECC8