$domain = "ADATUM.com"
$username = "$domain\myUserAccount"
$password = "myPassword!" | ConvertTo-SecureString -asPlainText -Force;
$credential = New-Object System.Management.Automation.PSCredential($username,$password)

$DomainJoinArgs = @{
  'DomainName' = $domain;
  'Credential' = $credential;
  'OuPath' = "";
  'Server' = "[servername here]";
}

Add-Computer @DomainJoinArgs -PassThru